THEORETICAL AND EXPERIMENTAL STUDIES ON

THE REACTIVITIES OF CONJUGATED KETENES

by

SIHYUN HAM, B.S.

A DISSERTATION

IN

CHEMISTRY

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

DOCTOR OF PHILOSOPHY

Approved

/

August, 1998

T y ACNOWLEDGEMENTS

' rt My deepest appreciation and respect go to Dr. David Birney who has

been the most desirable "boss" throughout all of my stay at Texas Tech. With

all of his guidance and help, especially with his constant motivation, but

mostly, with his complete trust, I have grown and accomplished much in

chemistry. I hope I can inspire and educate people in chemistry successfully

in my future as he did.

I greatly appreciate Dr. Richard Bartsch for introducing me to the

world of macrocyclic chemistry. His generous support and patience have

driven me to want to be a better chemist. Dr. Allan Headley has taught me a

great deal about reaction mechanisms. His kind advice and encouragement

always inspired me for new discoveries. Dr. Robert Walkup has broaden

much of my synthetic point of view. I have special thanks for Dr. Kwanghyun

No who imparted the beauty of chemistry to me and guided me into the

graduate program.

I want to express my thanks to many people in this department. I

appreciate Dr. Birney's group members, Bart Neff, Xiaomeng Huang,

Xiaolian Xu, Bill Shumway and Lubna Hammad, who shared friendship and

exciting moments of discoveries. I thank Mr. David Purkiss for taking 300

11

MHz iH NMR and 75 MHz i^C NMR for me. I also thank Dr. Bruce

Whittlesey for generously providing the X-ray crystal structure.

Many thanks are also due outside of chemistry. Most of all, nothing

would have come out without my dearest parents who have always provided

endless love and support. I have kept in mind one important lesson among

many from my parents throughout my graduate study, which was "Don't give

up". I thank for my two lovely brothers for their great affection and respect.

Many of my friends in Lubbock have helped me emotionally and spiritually.

Especially, the pastor, Kang Hoon Lee, and his wife, J in Yun Lee, and the

deaconess Jung Rye Kim and Yong Sun Oh have given their devoted love and

support for me.

Finally, I thank to the Robert A. Welch Foundation for the financial

support.

I l l

TABLE OF CONTENTS

ACKNOWLEDGMENTS ii

ABSTRACT ix

LIST OF TABLES xi

LIST OF FIGURES xiv

CHAPTERS

I. INTRODUCTION 1

1.1 Ketone 1

1.1.1 Historical Background 1

1.1.2 Structure and Properties 3

1.2 a-Oxoketene 8

1.3 References 16

PART ONE

THEORETICAL AND EXPERIMENTAL STUDIES

OF IMIDOYLKETENE

II. BACKGROUND 21

2.1 Generation and Direct Observation of Imidoylketene 21

2.2 Reactions of Imidoylke to no 29

IV

2.3 Previous Calculations on Imidoylketene 31

2.4 Characteristics of PericycHc Reactions 34

2.5 Characteristics of Pseudopericyclic Reactions 36

2.6 References 40

III. AN AB INITIO STUDY ON THE CONFORMATIONS AND REACTIONS OF IMIDOYLKETENE 43

3.1 Introduction 43

3.2 Computational Methods 45

3.3 Conformations of Imidoylketene 46

3.4 Addition of Water to Imidoylketene 51

3.5 Addition of Formaldehyde to Imidoylketene 59

3.6 Addition of Ammonia to Imidoylketene 65

3.7 1,3-Hydrogen Shifts 70

3.8 Conclusions 76

3.9 References 78

IV. CHEMOSELECTIVITY IN THE REACTIONS

OF IMIDOYLKETENE 82

4.1 Introduction 82

4.2 Competitive Reactions of Imidoylketene with Alcohols 83

4.3 Competitive Reactions of Imidoylketene with Cyclohexanone 89

4.4 Conclusions 92

4.5 References 94

V. EXPERIMENTAL 96

5.1 General Method 96

5.2 Solution Pyrolyses 97

5.3 GC Analysis 98

5.4 Competitive Reactions 100

5.4.1 Competitive Reactions of Imidoylketene with 1-Butanol and 2-Methyl-2-propanol 100

5.4.2 Competitive Reactions of Imidoylketene with 1-Butanol and Methanol 101

5.4.3 Competitive Reactions of Imidoylketene with 1-Butanol and 2,2,2-Trifluoroethanol 101

5.5 Syntheses of Authentic Materials 102

5.5.1 Synthesis of 3-Oxo-2-butenoic acid, butyl ester (2c) 102

5.5.2 Synthesis of 3-Propylamino-2-butenoic acid, 1,1-dimethylethyl ester (3a) 104

5.5.3 Synthesis of 3-Propylamino-2-butenoic acid, 1-methylethyl ester (3b) 105

5.5.4 Synthesis of 3-Propylamino-2-butenoic acid, 1-butyl ester (3c) 106

5.5.5 Synthesis of 3-Propylamino-2-butenoic acid, methyl ester (3d) 107

VI

5.5.6 Synthesis of 3-Propylamino-2-butenoic acid, trifluoroethyl ester (3e) 108

5.6 Synthesis of a Pyrroledione as an

Alternative Precursor 110

5.6.1 Synthesis of AT-Propyl imine (7b) 110

5.6.2 Synthesis of AT-Propyl li/-pyrrole-2,3-dione (8b) 111

5.7 References 113

PART TWO

AB INITIO STUDIES OF THE REACTIVITY

OF NITROSOKETENE

VI. BACKGROUND 115

6.1 References 119

VII. RESULTS AND DISCUSSION 120

7.1 Conformations of Nitrosoketene 120

7.2 Cycloadditions of Nitrosoketene 125

7.2.1 Formaldehyde Addition 129

7.2.2 Acetone Addition 131

7.2.3 Propenal Addition 134

7.3 Conclusions 136

7.4 References 138

vu

PART THREE

THERMAL CHELETROPIC DECARB0X\1^4TI0NS

\ a i l . BACKGROUND 141

8.1 References 148

IX. RESULTS AND DISCUSSION 150

9.1 Introduction 150

9.2 Computational Methods 151

9.3 Thermal Decarbonylation of Furandione 152

9.4 Thermal Decarbonylation of Pyrrole dione 156

9.5 Decarbonylations with One Orbital Disconnection 159

9.6 Conclusions 160

9.7 References 162

APPENDIX

A iH NMR, 13C NMR, X-RAY AND UV SPECTRA 164

B. SUPPLEMENTAL MATERIALS ON THE AB INITIO CALCULATIONS 188

vm

ABSTRACT

The reactivity of imidoylketene was examined using ab initio

molecular orbital theory. MP4(SDQ)/6-31G*//MP2/6-3lG* calculations on the

conformations of imidoylketene as well as transition states for several of its

reactions show parallels between the reactivity of imidoylketene and its

oxygen analog formylketene. All reactions proceed via concerted, planar (or

nearly so) transition structures regardless of the number of electrons

involved. Calculated activation energies are remarkably lower than those for

a pericyclic process, as expected from the case of formylketene. The reactions

are interpreted in light of their pseudopericyclic orbital topology.

A^-Propylacetacetimidoylketene was produced by the solution pyrolysis

of ^butyl AT-propyl 3-amino-2-butenoate. Selectivities of acetimdoylketene

toward various polar reagents were measured for the first time in a series of

competitive trapping reactions. Significant steric and electronic

discriminations of this ketone were observed, suggesting further

synthetically useful applications. These experimental reactivity trends

indirectly provide support for the planar, pseudopericyclic transition

structures predicted by ab initio calculations.

The mechanism of the reactions of nitrosoketene to form cyclic nitrones

(which leads stereoselective synthesis of a-amino acids) was investigated

using ab initio molecular orbital theory (MP4(SDQ)/6-31G*//MP2/6-31G* +

IX

ZPE). The direct [3+2] cycloadditions of nitrosoketene with ketones are

calculated to be favored over the alternative [4+2] pathway via concerted,

asynchronous, pseudopericycUc transition states. The detailed conformations

and the reactivity of nitrosoketene toward sterically and electronically

different ketones render useful information of the synthetic route for the

biologically important reactions.

Transition structures for a series of eight cheletropic decarbonylations

were optimized at the MP4(SDQ)/D95**//MP2/6-3lG* + ZPE level. Dramatic

differences in activation energies and in exothermicities are discussed in

terms of the molecular orbital topolog\'. A fundamental question regarding

pseudopericyclic orbital overlap is addressed, specifically, how many and

what t}-pe of orbital orthogonahties in the reaction sites are needed for a

reaction to be pseudopericyclic. Generalizations regarding the characteristics

of the pseudopericyclic reactions are made to provide a better understanding

of the "allowedness" and "favoredness" of the orbital topologies.

LIST OF TABLES

1.1 Experimentally Assigned IR Absorption Bands of Ketone (cm-i) 6

3.1 Relative Energies, Entropies, Dipole Moments and Low or Imaginary Frequencies of Structures Related to 1, Optimized at the MP2/6-31G** Level 47

3.2 Predicted Infrared Absorptions for Isomers of 1, at the MP2/6-31G** Level 50

3.3 Relative Energies, Entropies, Dipole Moments and Low or Imaginary Frequencies for the Water Addition to anti-Z-1, Optimized at the MP2/6-31G** Level 52

3.4 The Effect of Changing Nucleophiles to the Bond Extensions in the Transition State Geometries of Imidoylketene and Formylketene 61

3.5 Relative Energies, Entropies, Dipole Moments and Low or Imaginary Frequencies for the Formaldehyde Addition to anti-Z-1, Optimized at the MP2/6-31G** Level 63

3.6 Relative Energies and Entropies of Minima and the Transition Structure in the Addition of Ammonia to Imidoylketene, at the MP2/6-31G* Optimized Geometry 69

3.7 Relative Energies and Entropies of Minima and the Transition Structure in the Addition of Ammonia to Formylketene, at the MP2/6-31G* Optimized Geometry 69

3.8 Relative Energies, Entropies, Dipole Moments and Low or Imaginary Frequencies of Structures Related to 1, Optimized at the MP2/6-31G** Level 71

4.1 Results of Competitive Reactions of Pairs of Reagents with Acetimidoylketone (2) Generated by Pyrolysis of 3a in a Closed Vessel in Toluene Solution 85

XI

7.1 Absolute Energies of Z- and £J-Nitrosoketene in Hartrees. Optimized at the MP2/6-31G* Level 121

7.2 Relative Energies, Entropies, Dipole Moments of Z- and E-Nitrosoketene in kcal/mol. Optimized at the MP2/6-31G* Level 121

7.3 Vibrational Frequencies Calculated for both Z- and E-Nitrosoketene at the MP2/6-31G* Level 122

7.4 Relative Energies (kcal/mol) of Structures Optimized at the MP2/6-31G* Level 127

9.1 Relative Energies (in kcal/mol) for the Decarbonylation of Furandione, Optimized at the MP2/6-31G* Level 155

9.2 Relative Energies (in kcal/mol) for the Decarbonylation of Pyrroledione, Optimized at the MP2/6-31G* Level 158

A.l. Atomic coordinates (x 10 ) and equivalent isotropic o

displacement coefficients (AxlO^) 185

A.2. Bond lengths (A) 185

A.3. Bond angles («) 186 o

A.4. Anisotropic displacement coefficient (A^ xlO^) 186

A.5. H-Atom coordinates (x 10^) and isotropic displacement coefficients (A2 xlO^) 187

B.l Absolute Energies (Hartrees) of Conformations and Reactions of 1, Structures Optimized at the MP2/6-31G** Level 189

B.2 Absolute Energies in Hartrees of Stationary Points in the Addition of Formylketene and Ammonia at the MP2/6-31g* Optimized Geometry 190

x i i

B.3 MP2(FC)/6-31G** Optimized Cartesian Coordinates, Vibrational Frequencies (cm-i) and IR Intensities (km/mol) 191

B.4 Absolute Energies (Hartrees) of Conformations Optimized at the MP2/6-3IG* Level 208

B.5 Cartesian Coordinates Optimized at the MP2/6-31G* Level, Vibrational Frequencies and IR Intensities (km/mol) Optimized at the RHF/6-31G* Level 209

B.6 Absolute Energies (Hartrees) for the Decarbonylation of Furandione, Optimized at the MP2/6-31G* Level, unless otherwise indicated 222

B.7 Absolute Energies (Hartrees) for the Decarbonylation of Pyrroledione, Optimized at the MP2/6-31G* level, unless otherwise indicated 223

B.8 Cartesian coordinates, Vibrational Frequencies and IR Intensities (km/mol) Optimized at the MP2/6-31G* Level 224

xm

LIST OF FIGURES

1.1 Out-of-plane and in-plane molecular orbitals (HOMO and

LUMO) of ketone, 0=Ca=C6H2 4

1.2 Substituent effects on the structure of ketones 5

1.3 Resonance structures of ketone 5

2.1 Symmetry adapted molecular orbitals in the bonding changes occurring on the addition of water to formylketene 38

3.1 Mulliken charges, relative energies (kcal/mol), dipole moments (D), and entropies (cal/mol«K) of imidoylketene (MP2/6-31G** level) and formylketene (MP2/6-31G* level) 48

3.2 Resonance structures in anti-Z-1 and Z-2 49

3.3 Optimized geometries for the water addition to imidoylketene at the MP2/6-31G** level 54

3.4 Comparison between the calculated asynchronicities in the transition states of water addition to imidoylketene (MP2/6-31G** level) and formylketene (MP2/6-31G* level) 55

3.5 Optimized geometries for the formaldehyde addition to imidoylketene at the MP2/6-31G** level 60

3.6 Comparison between the calculated asynchronicities in the transition states of formaldehyde addition to imidoylketene (MP2/6-31G** level) and formylketene (MP2/6-31G* level) 62

3.7 Energy diagram for the addition reactions of imidoylketene computed the MP2(FC)/6-31G** level 64

3.8 MP2/6-31G** optimized structures for the addition of imidoylketene (12 and 13) and formylketene (15 and 16) 68

xiv

3.9 MP2/6-31G** optimized structures related to 1,3-hydrogen shifts of 1 '72

3.10 Resonance structures of 5a 73

3.11 Reaction barriers and exothermicities of 1,3-H shifts of conjugated ketones in kcal/mol 75

4.1 Transition states for the water additions with imidoylketene and formylketene optimized at the MP2/6-31G** and MP2/6-31G* level, respectively 87

7.1 Comparison of the computed IR spectra for Z-1 and E-1 with the experimental FTIR spectrum 124

7.2 Pseudopericyclic orbital interactions in 2TS 128

7.3 Geometries for [3+2] and [4+2] cycloaddition of nitrosoketene with formaldehyde, optimized at the MP2/6-31G* level 130

7-4 Geometries for [3+2] and [4+2] cycloaddition of nitrosoketene with acetone, optimized at the MP2/6-31G* level 132

7.5 Resonance structures in 2TS 133

7.6 Geometries for [3+2] and [4+2] cycloaddition of nitrosoketene with 2-propenal, optimized at the MP2/6-31G* level 135

8.1 Cheletropic decarbonylation of 3-cyclopentenone (1) 142

8.2 Orbital interactions in the decarbonylation of ITS 143

8.3 Cheletropic decarbonylation of bicyclo[2.2.1]hepta-2,5-dien-7-one (3) 144

8.4 Single orbital disconnection in the facile degenerate rearrangement of perfluoromethyl (Dewar thiophene S-oxide, 5) 146

XV

8.5 Possible orbital interactions in the nonlinear decarbonylation of cyclopropanone 147

9.1 Geometries for the decarbonylation of furandione, optimized at the MP2/6-31G* level 152

9.2 Out-of-plane and in-plane orbitals in the cheletropic decarbonylation of Furandione (1) 153

9.3 Geometries for the decarbonylation of pyrroledione, optimized at the MP2/6-31G* level 157

A. 1. iH NMR (300 MHz) spectrum of 3-oxo-2-butenoic acid, butyl ester (2c) and its tautomer (2c') 166

A.2. 13C NMR (75 MHz) spectrum of 3-oxo-2-butenoic acid, butyl ester (2c) and its tautomer (2c') 161

A.3. iH NMR (300 MHz) spectrum of 3-Propylamino-2-butenoic acid, 1,1-dimethylethyl ester (3a) 168

A.4. 13C NMR (75 MHz) spectrum of 3-Propylamino-2-butenoic acid, 1,1-dimethylethyl ester (3a) 169

A.5. iH NMR (300 MHz) spectrum of 3-Propylamino-2-butenoic acid, 1-methylethyl ester (3b) 170

A.6. 13C NMR (75 MHz) spectrum of 3-Propylamino-2-butenoic acid, 1-methylethyl ester (3b) 171

A.7. iH NMR (300 MHz) spectrum of 3-Propylamino-2-butenoic acid, 1-butyl ester (3c) 172

A.8. 13C NMR (75 MHz) spectrum of 3-Propylamino-2-butenoic acid, 1-butyl ester (3c) 173

A.9. iH NMR (300 MHz) spectrum of 3-Propylamino-2-butenoic acid, methyl ester (3d) 174

A. 10. 13C NMR (75 MHz) spectrum of 3-Propylamino-2-butenoic acid, methyl ester (3d) 175

xvi

A . l l . iH NMR (300 MHz) spectrum of 3-Propylamino-2-butenoic acid, trifluoroethyl ester (3e) 176

A. 12. 13C NMR (75 MHz) spectrum of 3-Propylamino-2-butenoic

acid, trifluoroethyl ester (3e) 177

A. 13. iH NMR (300 MHz) spectrum of iV-Propyl imine (7b) 178

A.14. 13C NMR (75 MHz) spectrum ofAT-Propyl imine (7b) 179

A.15. iH NMR (300 MHz) spectrum of iV-Propyl lii'-pyrrole-2,3-dione (8b) 180

A. 16. 13C NMR (75 MHz) spectrum of iV-Propyl lH-pyrrole-2,3-

dione (8b) 181

A.17. UV spectrum of AT-Propyl lif-pyrrole-2,3-dione (8b) 182

A. 18. X-Ray crystal structure of A^-Propyl l-?/-pyrrole-2,3-dione (8b), top view 183

A.19. X-Ray crystal structure of AT-Propyl liJ-pyrrole-2,3-dione (8b), side view 184

xvii

CHAPTER I

INTRODUCTION

1.1 Ketone

Since the identification of the first ketone in 1905, i the field of ketone

chemistry has expanded far beyond the initial expectations. A remarkable

amount has already been learned to broaden the horizon of ketone chemistry

after scientific controversy, dispute, disagreement and uncertainty. Many

scientists, authors and volumes have been dedicated to discoveries, the

organization of data and comprehensive coverage of entire field of ketone

chemistry-2-6

Ketones have been drawn much attention and interest not only

because of mechanistic and theoretical considerations, but also because of

their use of building blocks in organic synthesis. The next two sections will

briefly describe the history of 93 years of ketone chemistry and the general

introduction of the structure, bonding, and properties of ketones.

1.1.1 Historical Backerround

In 1905, diphenylketene (1) was prepared and characterized as the

first ketene by a German scientist, Hermann Staudinger.i The preparation of

1 involved the reaction of a-chlorodiphenylacetyl chloride with zinc."^ (eq 1.1)

Soon after this, dimethylketene (2)8 and dibenzopentafulvenone (3)^ were

prepared.

O Ph IT Zn y^c\

P'^Cl > = 0

1 (1.1)

Me

Me' ^)=-=0

The parent ketene (4) was prepared in 1907 by N. T. M. Wilsmore in

London from the pyrolysis of acetic anhydride using a hot platinum wire.^^

CH2=C=0

4

The discovery and investigation of ketones thereafter have blossomed

over decades regarding their utility and applications along with their

structural interests. Besides Staudinger, many Nobel laureates have been

interested in ketones, including R. B. Woodward, E. J. Corey, R. Hoffmann,

R. G. W. Norrish, K. Fukui, L. Ruzicka, O. Diels, G. Natta, and W. N.

Lipscomb. 6

Ketene has made a major contribution to organic synthesis. For

example, the formation of prostaglandin precursors, the synthesis of

quinones,ii.i2 and the formation of a /?-lactami3 leading to penicillin all

involved ketene in their major steps. For many years, the hydration of ketene

was a major industrial process for the preparation of acetic acid. Ketene is a

fascinating molecule and its usage is prominent with a bright future.

1.1.2 Structure and Properties

The most interesting character of the electronic structure of ketene is

tha t the highest occupied molecular orbital (HOMO) is placed perpendicular

to the lowest unoccupied molecular orbital (LUMO) in the ketene molecular

plane.6 This results in the positive charge on the a carbon next to the ketene

oxygen and the negative charge on the oxygen and the p carbon. Based on

this electronic feature, an electrophile is expected to approach in the plane of

the ketene molecule and a nucleophile is anticipated to attack perpendicular

to the molecular plane (Figure 1.1).

HOMO (out-of-plane)

. i l l l l H

electrophilic attack

LUMO (in-Plane)

nucleophilic attack

. . i l \ l H

Figure 1.1 Out-of-plane and in-plane molecular orbitals (HOMO and LUMO) of ketene, 0=0^=0^2.

Substituent effects on the structure of ketones have been reported

based on the ab initio molecular orbital calculations.i+i^ Ketones appeared to

be stabilized by electropositive substituents and destabilized by

electronegative substituents from the computed stabilization energies. This is

also in agreement with the calculated electronic structures. Extra

stabilization was found with 5 due to the conjugation^^ with the 7i-acceptor

substituent BH2, as shown in Figure 1.2. Ketones with electron donor

substituents (OH and NH2 in 6) adopt nonplanar geometries to minimize

repulsion between the substituents and the y carbon in ketene.^^-^^

H-B H-B; O; H^N >=^o — V-H^o© / = ^ o > = o

H H H H 5 6

Figure 1.2. Substituent effects on the structure of ketones

Experimental determinations of the molecular structures of ketones

have been reported using microwave,^^ electron diffraction's and X-ray

crystallographies^ techniques. There has been a rather good agreement

between the experimentally determined structures and the computed

structures, i^'i^

Many spectroscopic properties has been reported for the identification

of ketones. The most distinctive feature of the '^c NMR spectra of ketones is

a significant up field shift of the p carbon.20 This reflects a high electron

density at this carbon, as expected by the resonance structures shown in

Figure 1.3. The 'H NMR spectra also shows the high field position for the

proton on the /? carbon, reflecting the importance of the negative charge fiom

the resonance structure B.21

C=C=0 ^ ^ /C-G=0 R R

A B

Figure 1.3. Resonance structures of ketene

The infrared (IR) spectrum of ketene has been extensively studied. The

peak assignments for CH2=C=0, CHD=C=0 and CD2=C=0 are given in Table

1.1.22 The strong carbonyl stretching band between 2100 and 2200 c m ' is

used as the diagnostic for characterizing of ketones.

Table 1.1 Experimentally Assigned IR Absorption Bands of Ketene (cm')

Mode

C-H stretch

0 = 0 stretch

CH2 deformation

C=C stretch

C-H stretch (anti sym)

CH2 rocking

CH2 wagging

C=C=0 bending

C=C=0 bending (oopl)

CH2=C=0

3071

2152

1388

1118

3166

997

588

438

528

CHD=C=0

2268

2121

1228

890

2375

798

530

712

450

CD2=C=0

3115

2150

1293

1022

2297

815

. -_

. . .

515

Ultraviolet (UV) spectra of various ketones have been measured.23-25

The UV spectrum of the parent ketene, CH2=C=0 shows a C=C n^-n*

transition at 183 nm,23 as well as the C=0 TT -> TI* transition at 215 nm25 and

n ^ 71* transition at 325 nm. Substituent effects on the UV spectra of ketones

have not been systematically studied.

One of the earlier studies for the properties of ketene was to measure

the dipole moment.26 It was found that the dipole moment of ketene

(CH2=C=0) is 1.45 D, which is less than that of formaldehyde (CH2=0, 2.27

D) and acrolein (CH2=CHCH=0, 3.04 D). This result was interpreted by the

resonance contribution of structure B in Figure 1.3. An electron flow shifted

from the oxygen to y carbon would decrease the net dipole moment. Therefore

any electron withdrawing substituent on ketene would decrease the dipole

moment through the delocalization of the electron density from the p carbon.

It is observed tha t the dipole moment of CH2=CH-CH=C=0 (0.97 D)27 and in

BH2-CH=C=0 (1.08 D)i4 are both reduced from ketene itself, supporting the

importance of resonance contribution of structure B.

There have been numerous of studies on the preparation and reactions

of ketones from the beginning of this century. One of the most important

ketones is a-oxoketene. The earlier discoveries and investigations of a-

oxoketene produced in our laboratory lead us to study the related conjugated

ketones reported herein. The preparation and reactions of a-oxoketene will be

introduced in the following section.

1.2 a-Oxoketene

The acetylketene structure 8 was first proposed in 19071028 for the

ketene dimer which was later proven to be 7.29 f^g f j-st authentic a-

oxoketene 10 was synthesized in 1909 by the zinc dehalogenation of 9

(eq 1.2).

O^ H

7 8

Et02C II Zn EtO-

Br Et

9 10 (1.2)

Extensive studies of a-oxoketenes have been published during the last

few decades. Synthetically useful precursors to generate a-oxoketenes are 2-

diazo-l,3-dicarbonyl compounds, 1,3-dioxinones, fur an-2,3-dione s, keto esters

and acid chlorides.3i Representative reactions using each precursors are

introduced below.

8

From diazo compounds, a-oxoketenes have been generated and

detected under via the thermal and photoextrusion of nitrogen encountered

in the Wolff rearrangement (eq 1.3).32

O O

No

Aor hv

- N '

[4+2] adducts

P keto acid Trapping agent derivatives

O O

0

• •

Wolff rearrangement

O

R

R (1.3)

Mailer et al. successfully monitored the E and Z conformers of

formylketene (11) produced from 2-diazomalonaldehyde by IR and UV

spectroscopies in an argon matrix at 10K.33

IR: 2145 cm •1 IR: 2142 cm •1

The l,3-dioxin-4-ones have been precursors for the generations of a-

oxoketenes for more than 20 years.34 A wide variety of substituents on a-

oxoketones were obtained by the thermolysis or photolysis of l,3-dioxin-4-

ones (12) (eq 1.4).35 a-Oxoketenes undergo inter- and intramolecular

cyclizations to give y^lactams,36 2-furanones and 2-pyrrolones3' and

macrocylic lactones.38

R

R

O

O

12

O

\ 4 R

A or hv

O

R ^ ^ R ^

R^=H, Me, Et, Ph, F, CF3, COOR R^=H, Me

R \ R2=-(CH2)3-R^ R^=Me, -(CH2)5 -

R ^ ^ ^ '

R 2 ^

.0

Trapping Reactions

(1.4)

There are several reports on the generation and trapping of

acetylketene by thermolysis of 2,2,6-trimethyl-l,3-dioxin-4-one.39 However

only few reports of the direct observation of a-oxoketenes have been

published.'*^ '*' From flash vacuum pyrolysis (FVP) of the 1,3-dioxinone 13 at

350 °C, both the E and Z conformers of the acetylketene (14) were observed

10

by IR spectroscopy. Photolysis of 13 only gave the Z conformer in an Ar

matrix (eq 1.5).40

O

HoC y O _

CH3

CH3

13

FVP, 350 °C

H 3 C ^ 0 Z-14

IR:2143 cm'""

254nm, Ar, 12K y O

IR:2133cm -1

HoC^'^O (observed only) Z-14 (1.5)

Formylketene (11) is obtained as an intermediate in the thermolysis of

formyl Meldrum's acid (15), 2 as well as from 2,3-dioxin-4-one (16),^3 and is

trapped by various nucleophiles (eq 1.6).

11

o o

H^^V^O 0 ^ 0 "

15

O

-CO2

-\=o

\ CH3

CH3 16 ->=0

^ ^

H - ^ O

Z-11

O

O O

ROH H OH

O

O

- ^ \

(Me)2N-C=N

O

O

y ^N N(Me)2

(1.6)

The thermal decarbonylation of furan-2,3-diones 17 has been used

widely and favorably because the only byproduct is CO. a-Oxoketene was

easily observed by either the FVP or matrix photolysis of fur an-2,3-dione s

and was trapped by numerous nucleophiles (eq 1.7).44

- o A A O

18 IR: 2135-2148 cm

O R-N=C=N-R A , . . R

75% Ar / ^ O A ^

N-R

-1

(1.7)

12

One of the common precursors for the preparation of a-oxoketene is p-

ketoesters 19 via the enol form 20 with the extrusion of ROH. The ketene

intermediates have been trapped by nucleophiles.^0-45.46

R^C

0 0

V R^

19

^R3

R = R2=

R =

- 0 ^

= Alkyl : Alkyl, H : Me, Et

.H ' b

R 20

^R^

Aor hv

-R^OH O.

R'

R \

O

ROH 20

(1.8)

The mechanism of the decomposition of y^-ketoesters to form a-

oxoketenes have been investigated experimentally40.45 and theoretically.i^^'^^

There are two possibilities: retro [2+2] and retro [4+2] reactions (eq 1.9).

O O

R^O R^ \ retro [2+2]

H R 1 9 k

R^OXb

20

O

retro [4+2]

i o

R2 R^ 21

+ R^OH

(1.9)

13

When /?-ketoesters 19 in equilibrium with the enol form 20 were

pyrolysed in the gas phase where the tautomerization is slow, and trapped in

a matrix, unreacted 19, E and Z conformers of 21 and the alcohol byproduct

were observed. But none of the enols 20 were detected.^o 45 When

acetylketene and an alcohol in a matrix were warmed to -50 ~ -90 "C, only the

enol form 20 was observed, not the keto form 19. This experimental

observation is consistent with the proposed concerted [4+2] fragmentation.47

This unusual reactivity of acetylketene which favors [4+2] over [2+2]

reaction was elucidated by the ab initio calculations on the reactivity of

formylketene performed by Birney et alA^ The theoretical study on the

cycloaddition of formylketene with water and formaldehyde predicted a

pseudopericyclic orbital topology for the [4+2] pathway with a remarkably

low barrier and an unusual planar transition state.48

Based on the discoveries on the reactivity of the a-oxoketene, we have

conducted the theoretical and experimental studies on imidoylketene which

is closely related to a-oxoketene. This result provides a detailed insight into

the reactivity of the imidoylketene based on its structure and property. The

reactions of imidoylketene based on ab initio calculations and competition

experiments reported herein provide a better understanding of the

allowedness of the reaction mechanism. In addition, a synthetic application

14

for a biologically important systems based on the predictions made herein is

anticipated.

15

1.3 References

1. Staudinger, H. Chem. Ber. 1905, 38, 1735-1739.

2. Staudinger, H. Die Ketene; Verlag Enke: Stuttgart, 1912.

3. Hanford, W. E.; Sauer, J. C. Organic Reactions 1946, 3, 108-140.

4. Lacey, R. N. In The Chemistry of the Alkenes; Patai, S., Ed.; Interscience: New York, 1964; pp. 1161-1227-

5. Chemistry ofKetenes, Allenes, and Related Compounds; Patai, S., Ed.; Wiley: New york, 1980.

6. Tidwefl, T. T. Ketenes; John Wiley & Sons: New York, 1995.

7. Staudinger, H. From Organic Chemistry to Macromolecules; Wiley: New York, 1970.

8. Staudinger, H.; Klever, H. W. Chem. Ber. 1906, 39, 968-971.

9. Staudinger, H. Chem. Ber. 1906, 39, 3062-3067.

10. Wilsmore, N. T. M. J. Chem. Soc. 1907, 91, 1938-1941.

11. (a) Perri, S. T.; Moore, H. W.J. Am. Chem. Soc. 1990, 112, 1897-1905. (b) Xu, S. L.; Moore, H. W. J. Org. Chem. 1989, 54, 326-338. (c) Xu, S. L.; Moore, H. W. J. Org. Chem. 1992, 57, 326-338. (d) Xu, S. L.; Taing, M.; Moore, H. W. J. Org. Chem. 1991, 56, 6104-6109.

12. (a) Moore, H. W.; Decker, 0 . H. W. Chem. Rev. 1986, 86, 821-830. (b) Liebeskind, L. S.; Foster, B. S. J. Am. Chem. Soc. 1990, 112, 8612-8613.

13. (a) Ikota, N.; Hanaki, A. Heterocycles, 1984, 22, 2227-2230. (b) Bose, A. K.; Kapur, J.; Sharma, S.; Manhas, M. S. Tetrahedron Lett, 1973, 2319-2320. (c) Brady, W. T.; Gu, Y. Q. J. Org. Chem. 1989, 54, 2838-2842. (d) Ojima, I.; Chem, H.-J. C ; Qui, X. Tetrahedron, 1988, 44, 5307-5318. (e) Evans, D. A.; Williams, J. M. Tetrahedron Lett, 1988, 29, 5065-5068.

14. Gong, L.; McAlHster, M. A.; Tidwell, T. T. J. Am. Chem. Soc. 1991, 113, 6021-6028.

16

15. Allen, A. D.; Andraos, J.; Kregse, A. J.; McAllister, M. A.; Tidwell, T. T. J. Am. Chem. Soc. 1992, 114, 1878-1879.

16. McAllister, M. A.; Tidwell, T. T. J. Am. Chem. Soc. 1992, 114, 5362-5368.

17- Brown, R. D.; Godfrey, P. D.; MaNaughton, D.; Pierlot, A. P.; Taylor, W. H. J. Mol. Spec. 1990, 140, 340-352.

18. Rozsondai, B.; Tremmel, J.; Hargittai, I.; Khabashesku, V. N.; Kagramanov, N. D.; Nefedov, O. M. J. Am. Chem. Soc. 1989, 111, 2845-2849.

19. Biali, S. E.; Gozin, M.; Rappoport, Z. J. Phys. Org. Chem. 1989, 2, 271-280.

20. Firl, J.; Runge, W. Z. Naturforsch. 1974, 29B, 393-398; Ajigew, Chem.,

Int. Ed. Engl. 1973, 12, 668-669.

21. Masters, A. P.; Sorensen, T. S.; Ziegler, T. J. Org. Chem. 1986, 51, 3558-

3559

22. Leszczynski, J.; Kwiatkowski, J. S. Chem. Phys. Lett. 1993, 201, 79-83.

23. Price, W. C ; Teegan, J. P.; Walsh, A. D. J. Chem.Soc. 1951, 920-926.

24. Rabalais, J. W.; MacDonald, J. M.; Schorr, V.; MaGlynn, S. P. Chem.

Revs. 1971, 71, 73-108.

25. Kirmse, W. Carbene Chemistry, 2nd ed.; Academic: New York, 1971; p. 9.

26. Hannay, N. B.; Smyth, C. P. J. Am. Chem. Soc. 1946, 68, 1357-1360.

27. Brown, R. D.; Godfrey, P. D.; Woodruff, M. Aust. J. Chem.. 1979, 32,

2130-2109.

28. Stewart, A.; Wilsmore, N. Nature London, 1907, 75, 510.

29. Hurd, C ; Blanchard, C. J. Am. Chem. Soc. 1950, 72, 1461.

30. Staudinger, H.; Bereza, S. Chem. Ber. 1909, 42, 4908-4918.

17

31. Wentrup, C ; Heilmayer, W.; KoUenz, G. Synthesis 1994, 1219-1248.

32. Meier, H.; Zeller, K. P. Angew, Chem. Int. Ed. Engl. 1975, 14, 32.

33. Maier, G.; Reisenauer, H. P.; Sayrac, T. Chem. Ber. 1982, 115, 2192.

34. Jager, G.; Wenzelburger, J. Liebigs Ann. Chem. 1976, 1689.

35. (a) Wentrup, C ; Heilmayer, W.; KoUenz, G. Synthesis 1994, 1219-1248. (b) Kappe, C. O.; Wong, M. W.; Wentrup, C. J. Org. Chem. 1995, 60, 1686-1695.

36. Sato, M.; Ogasawara, H.; Takayama, K.; Kaneko, C. Heterocycles 1987, 26, 2611.

37- Sakaki, J.; Sugita, Y.; Sato, M.; Kaneko, C. Tetrahedron 1991, 47, 6197.

38. Boeckman, Jr., R. K ; Pruitt, J. R. J. Am. Chem. Soc. 1989, 111, 8286.

39. Clemens, R. J. Chem. Rev. 1986, 86, 242.

40. Freiermuth, B.; Wentrup, C. J. Org. Chem. 1991, 56, 2286.

41. Clemens, R. J.; Witzman, J. S.; J. Am. Chem. Soc. 1989, 111, 2186, and the reference therein.

42. Sato, M.; Yoneda, N.; Katagiri, N.; Watanabe, H.: Kaneko, C. Synthesis 1986, 673.

43. Sato, M.; Yoneda, N.; Kaneko, C. Chem. Pharm. Bull. 1986, 34, 621, 4577.

44. (a) Andreichikov, Y. S.; KoUenz, G.; Kappe, C. O.; Leung-Toung, R.; Wentrup, C. Acta Chem. Scand. 1992, 46, 683. (b) Andreichikov, Y. S.; Yu, S. Org. Khim. 1988, 24, 458.

45. Witzeman, J. S. Tetrahedron Lett. 1990, 31, 1401-1404.

46. Coleman, R. S.; Fraiser, J. R. J. Org. Chem. 1992, 57, 4850-4858.

47- AUen, A. D.; Gond, L.; TidweU, T. T. J. Am. Chem. Soc. 1990, 112, 6396-6397.

18

48. Birney, D. M.; Wagenseller, P. E. J. Am. Chem. Soc. 1994, 116, 6262-6270.

19

PART ONE

THEORETICAL AND EXPERIMENTAL STUDIES

OF IMIDOYLKETENE

20

CHAPTER II

BACKGROUND

2.1 Generation and Direct Observation of Imidovlketene

In contrast to the long history of a-oxoketenes (since 1907), it was

only in 1964 that the imidoylketene 2 was first suggested to be a conceivable

intermediate. This was in the Conrad-Limpach reaction 2 for quinone

synthesis (eq 2.1).3

Ph -Np7)=0 H~>0

Et

EtOH

Q

N' (2.1)

In 1966, the photochemical conversion of 3-phenyl-3,4-dihydro-4-

oxobenzo-l,2,3-triazine (4) to yield acridone (5) was observed upon irradiation

o

with ultraviolet light above 3000A in benzene.4 The product 5 was

characterized by its infrared (IR) spectrum. For the reaction mechanism, the

imidoylketene 6 was considered as a possible intermediate (eq 2.2).

21

o

N'

4

N' I

N

•Ph hv

Ph (2.2)

Formation of the imidoylketene intermediate 9 was postulated for the

cycloaddition reaction of sulfinamide anhydride 7 with amides for the

synthesis of corresponding quinazolin-4-ones 10 in 1976. ^ However, a

multistep reaction mechanism via intermediate 8 without the participation of

the imidoylketene was proposed to be more probable due to the mild reaction

conditions (80 ^C) (eq 2.3).

HN

O

O

N H

O

.SO

SO'

O

HN d SO2H

8

O

-SO- O

NH

<y N

H2N o

HoO

O

N

10

X)

(2.3)

22

The preparation and observation of imidoylketenes have been studied

more systematically since the middle of the 1980s. The generation and

reactions of imidoylketenes have been recently reviewed. ^ Synthetically

useful procedures for the generation of imidoylketenes are primarily: (a)

thermolysis or photolysis of Meldrum's acid derivatives; (b) thermal

decarbonylation of pyrrole-2,8-diones; and (c) elimination of alcohols from

enamino esters (Scheme 2.1). The imidoylketenes are usually generated from

the corresponding precursors in situ and trapped. To isolate and examine

unstable imidoylketenes, flash vacuum pyrolysis (FVP) and matrix photolysis

are used.

0 ^ 0

O O

K NR

O HN .R

Aor hv

CO2 (CH3)2=0

-CO

-ROH

R y o

R^N I

R

Scheme 2.1. General precursors for the generation of imidoylketene

23

Meldrum's acid derivatives have been used as precursors to generate

and observe imidoylketenes. - ^ The thermal decomposition of 5-

[(arylamino)methylidene]-l,3-dioxane-4,6-diones 11 to give 4-

hydroxyquinolines/4-quinolones 14 was studied by FVP at temperatures

between 400 and 600 ^C (10 - -10 -3 torr) in 1984.6 The imidoylketene 13 and

(aminomethylene)ketene 12 intermediates were first isolated and observed at

-196 °C on KBr or BaF2 windows by a direct IR spectroscopic examination

(eq 2.4).

0^0

oAAo \

11 X = H , CH3, OH

400 -600 °C

-CO2 - (CH3)2=0

14

1,3-H-

O

HV^

H^N-13

r ^ ^ ^

(2.4)

The FVP of another Meldrum's acid derivative 18 also allowed the

observation of imidoylketenes. ^ At the lower pyrolysis temperatures (380-440

oC), two ketenes were observed and identified as the carboxy(imidoyl)ketene

24

16 (2150 cm-i, 2500-3200 cm-i) and the imidoylketene 17 (2120 cm-i). At the

pyrolysis temperatures 440 ^C, the methyleneketene 19 started to apprear

(2080 cm-i) (eq 2.5).

y 0 0 , / O

>380°C, H O O C ^ ^ O OH

^ N

15

X O O

(CH3)2=0 T ^ N

> 440 X

O - ->y ^o - CO2 I - (CH3)2=0

NH

18

16

O

NH

19

-CO2 > 380 °C

1,3-H-

Q

N

17

(2.5)

The generation of the imidoylketene 21 from Meldrum's acid derivative

20 at 400-500 °C (10 - mbar) was observed in an Ar matrix by IR spectra,

including its rearrangement to ketenimine 22 (eq 2.6).^^ At higher

temperature (> 500 ^C), 21 (2132 cm-i) decreased and 22 (2076 cm-i)

increased in intensity (eq 2.6). When 22 was washed from a 77 K cold finger

with CHCI3 containing 1% ethanol, thioester 23 was obtained in 78% yield.

25

0^0

oAAo MeS N-Me

20 ^

H SMe

O

EtO'

23

N^ Me

H

400-500 °C

-CO2 - (CH3)2=0

EtOH

/

O

S NMe

Me 21

1.3-MeS-

O

A SMe

NMe 22

(2.6)

Imidoylketenes are also conveniently generated by F \ T of pyrrole-2,3-

diones. 1 -13 Thermal CO extrusion from pyrrole-2,3-diones 24 at 500-700 °C

(10 -4 mbar) (1 bar = 10^ Pa) gave imidoylketene 25 which was observed by IR

spectroscopy at 77 K (eq 2.7). 12a Isolation of the products on a KBr disk gave

only the quinolones 26.

R.

Ph'

O X)

^>r\ 500-700°c R v ^ I > = 0 •

' " '^N -CO _. ^ . _ . N I

Ph 24

Ph^^^NPh

25

R=H, Me, Et, Br, CN

(2.7)

26

A^-Adamantylimidoylketene 28 produced from pyrroledione 27 by FVP

was monitored by direct on-line mass spectrometry and by IR spectroscopy in

an Ar matrix at 18 K or as neat soUds at 77 K.i2b Under the thermal

condition, 28 is in equilibrium with azetin-2-one 30 and also undergoes a

rearrangement to form oxoketen imine 29.

p

Ph-^^^N Ad

27

400-750 °C Me. /

° -CO ^

Ph^^NAd

28 2113 cm'''

A,>340 nm

Me

Ad = 1-Adamantayl

i -

A

y ^ N Ph^ Ad

30 1814

1,3-Ph->-

A

, 1819 cm

^^Y^Ph 1

NAd

29 2035 cm -1

(2.8)

The thermolysis of enaminoesters 31 also generated imidoylketenes 32

and 34 as intermediates to give rearrangement and dimerization products

(33 and 35, respectively) without any trapping agents in the gas phase (eq

2.9). 14

27

R—CH2CH2CH3

O

A N^ I

R 31

OEt_

H

> 400 °C -EtOH

R=C(CH3)3

> 450 °C -EtOH

O

N

'^N

32

O

1,5-H-

and I.S-H-

N "O

35

(2.9)

The imidoylketene intermediate 37 was also generated from

thermolysis of cyclic enaminoesters 36. Subsequently, 37 underwent a series

of intramolecular thermal rearrangements (eq 2.10).!^

O

a OEt

N^^

K OH

36 R

O II

CH K O

R

330 °C

•EtOH

1,5-H-

O 11

CH

N

R' OH

R

(2.10)

28

The reactions of dipenylcyclopropenone (38) with A^-aminopyridinium

iodide is proposed to involve the imidoylketene (39) as an intermediate which

gives 4-pyrimidone derivatives (eq 2.11).i6

NH.

Et.N

38

Ph

Ph O'

HN-S^_^

Ph y O

Ph^'^NH

39

(2.11)

2.2 Reactions of Imidovlketene

As described above, imidoylketenes undergo intramolecular

rearrangements depending upon the substituents. With an aromatic amino

substituent, the imidoylketene undergoes efficient electrocyclization to give

quinolones (eq 2.4, 2.7). With an aliphatic amino substituent, an a-hydrogen

atom of the amino group undergoes 1,3- or 1,5-hydrogen shifts (eq 2.12, 2.13).

7-11,14,15 However, imidoylketenes dimerize if they cannot rearrange (eq 2.9).i4

CH3N H

1,5-H~

O

" - . / H

y\ N H II CH2

(2.12)

29

»y Q O

H^N-K 1,5-H-

H *-H

H ^ N

H 1,3-H-(2.13)

The following electrocyclization reaction of imidoylketene was reported

(eq2.14). i

R

N ^O

R' O

R

N ^ O

R hv (270)

hv (254) p2.

N-

'O hv (254) R

• 0

^ ^

H H O (2.14)

R^=C(CH3)3 R^=CH3

R =CF3 R =CH3

R^=H R2=H

AT-AUylimidoylketene 41 generated from y^-enaminooster 40 undergoes

intramolecular [2+2] cycloaddition reactions giving 42 in the gas phase.^8

30

H N^/^

YOB O 40

R=Alkyl

EtOH

O [2+2]

42

(2.15)

There are only a few reports concerning bimolecular reactions of

imidoylketene. There is only one report of trapping imidoylketene with an

aldehyde; in 43 the imidoylketene is more reactive than the a-oxoketene

moiety (eq 2.11). i3b

O p-BrC6H4CHO

BrC6H4" ^O^^O (2.16)

2.3 Previous Calculations of Imidovlketene

Imidoylketene can exist in four different conformations. Nguyen, Ha,

and More O'Forrall reported the energies of two of the possible conformations

(anti-Z-44 and anti-£J-44) in the parent system (eq 2.17) and the transition

state for its ring closure to give the four-membered ring azetone 47. i

31

Q N-H

/ /

anti-Z-44

anti-E-44

Q. H

45

Q. ,H Q -N ^ ^

46

.H N

47

(2.17)

Relative energies (kcal/mol) MP4(SDQ)/6-31G**//RHF/6-31G**+ZPE

0.0 (Z-44) 0.3 (E-44)

24.4 (45) 15.7 (46) 9.9 (47)

The resufts (MP4(SDQ)/6-3lG** energies at RHF/6-31G** geometries

with zero-point vibrational frequency corrections) indicate that Z-44 is

slightly favored (0.3 kcal/mol) relative to -E-44, even though the former has a

larger dipole moment (3.2 D) than the latter (1.2 D). However, no explanation

was given for the origin of the observed preference. The planar structure

azetone 46 was found and characterized as a transition state for nitrogen

inversion to form pyramidal structure 47 with the barrier of 5.8 kcal/mol.

Remarkably, the transition state 45 for the ring opening was planar.

Although the authors did not mention on it, the planar TS geometry is

unusual for the electrocyclic ring opening which generally requires a twisting

between two ends of the breaking a-bond in order to overlap with the n-

orbital. 20.21 The isoelectronic ring opening of formylketene^^ has been

32

interpreted as pseudopericyclic orbital topology by Birney et al (eq 2.18).22

The remarkably low activation barrier of 2.5 kcal/mol (computed at the

MP4(SDQ/6-31G* +ZPE level) for the ring-opening of/^-lactone 49 was

discussed in Ught of the low calculated exothermicity (18.9 kcal/mol) and the

planar transition structure.

Q P

R R

Z-48

O.

y R R

Vo > < (2.18)

R R

49

The elimination of acetone from 50 yielding acetimidoylketene 51 was

calculated at the RHF/6-31G* level. 23 The transition state for the reaction

adapts almost a planar geometry, because the electron-electron repulsion

inherent in a pericyclic reaction can be avoided in the pseudopericyclic orbital

topology.

O

N

51

O

(2.19)

33

The following section will describe the definitions and the

characteristics of pericyclic and pseudopericyclic reactions.

2.4 Characteristics of Pericyclic Reactions

R. B. Woodward and R. Hoffmann developed the concept of pericyclic

reactions 20 and defined them as "reactions in which all first-order changes in

bonding relationships take place in concert on a closed curve."24 They

categorized the reaction types into five areas: electrocyclic reactions,

cycloadditions, sigmatropic shifts, cheletropic reactions, and group transfer

and oHmination reactions. They discovered the principles of orbital symmetry

conservation showing which reactions could be allowed and forbidden.

Allowed reactions are not required to be concerted; however, the

concerted aUowed pathway generaUy maintains maximum bonding overlap

unless there are some factors destabilizing the concerted reaction path. This

is another importance of the orbital symmetry which is the fi'ontier orbital

theoiy in pericycUc reactions discovered by Fukui.25 In the frontier orbital

theory, reactions are aUowed only when aU overlaps between the highest-

occupied molecular orbital (HOMO) of one reactant and the lowest-

unoccupied molecular orbital (LUMO) of the other are such that a positive

lobe overlaps only with another positive lobe (bonding) and a negative lobe

with another negative lobe (bonding). AUowed reactions can maintain

34

bonding all along a concerted pathway, while forbidden reactions necessarily

have antibonding orbital overlap along the reaction pathway. Pericyclic

reactions often have low barriers due to a maximum bonding orbital overlap

in the concerted allowed pathway, although the barriers are often

substantial.

The transition state geometries for the allowed pericyclic reactions of

hydrocarbons are usually not planar. The concerted pericyclic pathway

maintains bonding between the interacting orbitals and maximizes overlap of

the interacting orbitals. The desirable geometries for the transition states of

pericyclic orbital overlap are not planar to maintain the closed loop around

the cyclic orbital overlap.

Another important concept regarding the allowed concerted pericyclic

transition states are the selection rules developed by Dewar26 and

Zimmerman.2"^ This concept is based on the criterion for deciding whether a

process is allowed or forbidden, and whether the transition state is stabilized

(aromatic character) or destabilized (antiaromatic character). The rule is that

the "allowedness" of the reaction depends on the number of electrons involved

in a Hiickel or Mobius orbital overlap at the transition states.28 Application of

those fundamental principles of the orbital theory have provide new insight

into pericyclic reactions and have also opened new fields of experimental

investigation.

35

The next section will describe the subset of pericyclic reactions which

is most interest "pseudopericyclic reactions" for us.

2.5 Characteristics of Pseudopericyclic Reactions

The term "pseudopericyclic" was first described by Lemal et al. 29 Their

full definition was "a concerted transformation whose primary changes in

bonding compass a cyclic array of interchange roles. In a crucial sense, the

role interchange means a 'disconnection' in the cyclic array of overlapping

orbitals because the atomic orbitals switching functions are mutually

orthogonal. Hence pseudopericyclic reactions cannot be orbital symmetry

forbidden." This concept originally came out from the degenerate

rearrangement of molecule 52, with the exceptionally low barrier of 6.8

kcal/mol. (eq 2.20)

/P /O 8- 8"

^ 3 C ^ / ^ , p . _ = ^ ^ 3 C ^ , , £ I ^ 7 - C F 3 - ^ r ^ ^ = < ^^3 (2.20) " 3 ^^^ ^CF3

52 52

Despite of this foundation of the rather unusual rearrangement, no

clear explanation has been made for the orbital topology of pseudopericyclic

reactions.30 Recently, Birney et al. have examined this concept thoroughly

36

using ab initio molecular orbital theory and developed the fundamental

principles of the pseudopericyclic reactions for the first time.22.32 The

following generalizations32f were made from the extensive theoretical studies

on a variety of thermal pseudopericyclic reactions including

cycloadditions,22,32a-c,e sigmatropic rearrangements,32d,e and

electrocyclizations.22.32d

1. "A pseudopericyclic reaction is orbital symmetry allowed via a pathway

that maintains the orbital disconnections, regardless of the number of

electrons involved." This is NOT an exception of the conservation of

orbital symmetry by Woodward and Hoffmann. There are two sets of

orbital interactions: in-plane and out-of-plane orbital overlaps. Since there

is a disconnection between these sets of orbitals, no electrons transfer to

each other. Therefore counting electrons for allowedness of reactions

becomes irrelevant. Birney et al. have provided the first distinctive

example of pseudopericyclic orbital topology for the [4+2] cycloaddition of

water to formylketene (Figure 2.1).32a

37

o J

O

I

, 'H

O

OH

out-of-plane (6 electrons)

D-H -H -H

in-plane (8 electrons)

Figure 2.1. Symmetry adapted molecular orbitals in the bonding changes occurring on the addition of water to formylketene

2. 'Barriers to pseudopericyclic reactions can be very low, or even non-existent,

(a) if there is a good match between nucleophilic and electrophilic sites in

reactants. (b) if the geometrical constraints of the system allow for

appropriate angles in the transition states, in close analogy to Baldwin's

rules, and (c) if the reactions is exothermic." The origin of the barrier of

pericyclic reactions involves the unavoidable electron-electron repulsion

between interacting orbitals from the aromatization of the transition

38

states.33 Since the Dewar-Zimmerman transition state aromaticity26.27

becomes irrelevant due to the lack of cyclic orbital overlap, the

unavoidable electron-electron repulsion between interacting orbitals can

be avoided in the transition states and the overall barrier can become

lower than usual pericyclic reactions.

3. "Pseudopericyclic reactions will have planar transition states if possible.

However, crowding at the transition state can lead to small distortions

from planarity. This is in contrast to typical all-hydrocarbon pericyclic

reactions for which the need to maintain orbital overlap leads to nonplanar

transitions states." As shown in Figure 2.1, there is no or little overlap

between out-of-plane (TI) and in-plane (o and 7i) orbitals. With this

disconnection in the interacting orbital overlaps, Fukui's rules based on

the frontier orbital theory become irrelevant. Although HOMO-LUMO

bonding interactions are still relevant, a distorted transition state

geometry is not required because it is not necessary to maintain without a

closed loop of orbitals in a pseudopericyclic transition state. Overall, the

transition state structures adapt planar or nearly planar geometries to

maximize truly efficient orbital overlap and stabilizing bonding of

interacting in-plane and out-of-plane orbitals.

39

3.9 References

1. (a) Wentrup, C ; HeUmayer, W.; Kollenz, G. Synthesis 1994, 1219-1248. (b) Hyatt, J. A.; Raynolds, P. W. In Organic Reactions; L. A. Paquette, Ed.; John Wiley & Sons: 1994; Vol. 45; pp 159-636. (c) TidweU, T. T. Ketenes; John WUey & Sons: New York, 1995..

2. (a) Conrad, M.; Limpach, L. Ber. 1888, 21, 523. (b) Conrad, M.; Limpach, L. Ber. 1887, 20, 944.

3. Blatter, H. M.; Lukaszewski, H. Tetrahedron Lett. 1964, 825-861.

4. Burgess, E. M.; Milne, G. Tetrahedron Lett. 1966, 93-96.

5. (a) Kametani, T.; Higa, T.; Loc, C. V.; Ihara, M.; Koizumi, M.; Fukumito, K. J. Am. Chem. Soc. 1975, 98, 6186-6188. (b) Kametani, T.; Loc, C. V.; Higa, T.; Koizumi, M.; Ihara, M.; Fukumito, K. J. Am. Chem. Soc. 1976, 99, 2306-2309.

6. Briehl, H.; Lukosch, A.; Wentrup, C. J. Org. Chem. 1984, 49, 2772-2779.

7. (a) Wentrup, C ; Briehl, H.; Lorencak, P.; Vogelbacher, U. J.; Winter, H.-W.; Maquestiau, A.; Flammang, R. J. Am. Chem. Soc. 1988, 110, 1337-1343. (b) Gordon, H. J.; Martin, J. C ; McNab, H. J. Chem. Soc, Chem. Commun. 1983, 957-958 (c) Gordon, H. J.; Martin, J. C ; McNab, H. J. Chem. Soc, Perkin. Trans. I. 1984, 2129-2132

8. Grandjean, D.; Dhimane, H.; Pommelet, J . -C; Chuche, J. Bull. Soc. Chim. Fr. 1989, 126, 657-660.

9. Cheikh, A. B.; Chuche, J.; Manisse, N.; Pommelet, J. C ; Netsch, K.-P.; Lorencak, P.; Wentrup, C. J. Org. Chem. 1991, 56, 970-975.

10. Kappe, C. O.; Kollenz, G.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 487-490.

11. Chuburu, F.; Lacombe, S.; GuUouzo, G. P.; Wentrup, C. New. J. Chem. 1994, 18, 879-888.

40

12. (a) Kappe, C. O.; Kollenz, G.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 485-486. (b) Kappe, C. O.; Kollenz, G.; Netsch, K.-P.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 488-490.

13. (a) Maslivets, A. N.; Krasnykh, O. P.; Smirnova, L. I.; Andreichikov, Y. S. J. Org. Chem. (USSR) 1989, 941-948. (b) Aliev, Z. G.; Maslivets, A. N.; Krasnykh, O. P.; Andreichikov, Y. S.; Atovmyan, L. O. Russian Chemical Bulletin 1993, 42, 1569-1572.

14. Maujean, A.; Marcy, G.; Chuche, J. Tetrahedron Lett. 1980, 21, 519-522.

15. Grosdemange-Pale, C ; Chuche, J. Bull. Soc Chim. Fr. 1989, 126, 644-649.

16. Gilchrist, T. L.; Harris, C. J.; Roes, C. W. J. Chem. Soc, Chem. Commun. 1974, 487-488.

17. (a) Maier, G.; Schafer, U. Tetrahedron Lett. 1977, 18, 1053-1056. (b) Hoppe, A. K. J. Am. Chem. Soc 1975, 97, 6590-6591.

18. Arya, F.; Bouquant, J.; Chuche, J. Tetrahedron Lett. 1986, 27, 1913.

19. Nguyen, M. T.; Ha, T.; More O'FerraU, R. A. J. Org. Chem. 1990, 55, 3251-3256.

20. Woodward, R. B.; Hoffmann, R. Uie Conservation of Orbital Symmetry; Verlag Chemie, GmbH: Weinheim, 1970.

21. (a) Kallel, E. A.; Wang, Y.; Houk, K. N. J. Org. Chem. 1989, 54, 6006. (b) Spellmeyer, D. C ; Houk, K. N. J. Am. Chem. Soc 1988, 110, 3412. (c) Rydolf, K.; Spellmeyer, D. C ; Houk, K. N. J. Org. Chem. 1987, 52, 3708-3710.

22. Birney, D. M.; Wagenseller, P. E. J. Am. Chem. Soc 1994, 116, 6262-6270.

23. Eisenberg, S. W. E.; Kurth, M. J.; Fink, W. H. J. Org. Chem. 1995, 60, 3736-3742.

41

24. Woodward, R. B.; Hoffmann, R. Angew. Chem. Int. Ed. Engl. 1969, 8, 781.

25. (a) Fukui, K. Tetrahedron Lett. 1965, 2009. (b) Fukui, K. Ace Chem. Res. 1971, 4, 57.

26. Dewar, M. J. S. The Molecular Orbital Theory of Organic Chemistry: McGraw-HiU Book Company: New York, 1969; pp 316-339.

27. (a) Zimmerman, H. J. Am. Chem. Soc. 1966, 88, 1564. (b) Zimmerman, H. Ace Chem. Res. 1971 4, 272.

28. In the Ti-orbitals in the cyclic array of transition state, Hiickel overlap has zero or an even number of sign inversions and Mobius overlap has one or odd number of sign inversions.

29. Ross, J. A.; Seiders, R. P.; Lemal, D. M. J. Am. Chem. Soc 1976, 98, 4325-4327.

30. There were attempts to understand the pseudopericyclic orbital interactions.31

31. (a) Snyder, J. P.; Halgren, T. A.; J. Am. Chem. Soc 1980, 102, 2861-2863. (b) Dewar, M. J. S.; Healy, E. F.; Ruiz, J. Pure Appl. Chem. 1986, 58, 67-74.

32. (a) Ham, S.; Birney, D. M. Tetrahedron Lett. 1994, 35, 8113-8116. (b) Wagenseller, P. E.; Birney, D. M.; Roy, D. J. Org. Chem. 1995, 60, 2853-2859. (c) Ham, S.; Birney, D. M. J. Org. Chem. 1996, 61, 3962-3968. (d) Birney, D. M. J. Org. Chem. 1996, ^i ,243. (e) Matsui, H.; Zuckerman, E. J.; Katagiri, N.; Sugihara, T.; Kaneko, C ; Ham, S.; Birney, D. M. J. Phys. Chem. A 1997, 101, 3936-3941. (f) Birney, D. M.; Ham, S.; Unruh, G. R. J. Am. Chem. Soc 1997, 119, 4509-4517. (g) Ham, S.; Birney, D. M. Tetrahedron Lett. 1997, 38, 5925-5928. (h) Birney, D. M.; Xu, X.; Ham, S. J. Org. Chem. 1997, 62, 7114-7120.

33. Houk, K. N.; Candour, R. W.; Strozier, R. W.; Rondan, N. G.; Paquette, L. A. J. Am. Chem. Soc 1979, 101, 6797-6802.

42

CHAPTER III

AN AB INITIO STUDY ON THE CONFORMATIONS

AND REACTIONS OF IMIDOYLKETENE

3.1 Introduction

Imidoylketene (1) is electronically similar to formylketene (2). Both

substituents on ketenes contain conjugated 7c-systems with out-of-plane

ketene 7r-system in addition to the in-plane lone pair on N5 and 05 . Those

ketenes have been used for the application of synthetically useful reactions.

Z-1 Z-2

We have been interested in the mechanisms of various reactions

involving conjugated ketenes.2 An important and unusual characteristic of

the reactivity of these conjugated ketenes is their tendency to participate in

[4+2]3 reactions instead of involving in the [2+2] reactions which are typical

43

for ketenes.4-6 From the theoretical studies in conjugated ketenes, we have

shown that the in-plane lone pair in ketenes participated in the reactions

which allow to have the pseudopericyclic orbital topology.2."^

Although imidoylketene undergoes a variety of synthetically important

reactions, there have been no systematic studies on the detailed

conformational and mechanistic studies on the reactivity of imidoylketene.

Therefore, we have carried out ab initio molecular orbital theory calculations

to explore the detailed conformations and several reactions of imidoylketene

(Scheme 3.1). This provides insight into the similarities and differences in

reactivities between imidoylketene and formylketene as well as the synthetic

application of these reactions.

O

X X

XH

NH 3a O 3b

HoO O

^

anti-Z-1 Z-2

CH2O O

o

"X

4a 4b

J

H

X X X

X A' N-H O CH2

O 1.3-H

5a 5b 5c

anti-E-1 E-2

1,3-H -

6a 6b 6c

Scheme 3.1

44

3.2 Computational Methods

The ab initio molecular orbital calculations were carried out using

Gaussian 92.8 Geometry optimizations were performed first at the RHF/6-

31G* level and then at the MP2(FC)/6-31G** level. MP2 optimizations give

reasonable agreement with MCSCF geometries for orbital symmetry allowed

(but not forbidden) pericyclic reactions.^ Frequency calculations were

performed to verify the identity of each stationary point as a minimum or

transition state. Single point energies of each structure were obtained at the

MP4(FC,SDQ)/6-3lG** level. The zero-point vibrational energy (ZPE)

corrections were obtained by scaling the MP2/6-31G* ZPE by 0.9646, as

recommended by Pople et al.^^ Unless otherwise mentioned, all energies

discussed in the text are MP4(SDQ, FC)/6-31G** with the ZPE correction.

FuU geometries, vibrational frequencies and absolute energies are reported in

the supplementary material at the end of this dissertation.

The 6-3IG** basis set, which provides polarization functions on the

hydrogens, was used because of the hydrogen transfer reactions involved. The

MP4 procedure with triple excitations does lower the computed absolute

energies. However, it does not alter the relative energies of ketenes in our

experiences.2c.e For economy of computational cost, the single point energies

were calculated at the MP4(SDQ) level afterwards.

45

3.3 Conformations of Imidovlketene

Two conformations of imidoylketene, Z and E were optimized by

Nguyen et aZ. i even though there are actually four different conformations of

the imidoylketene; Z and E around the C-C bond, syn and anti around the C-

N bond. All four are optimized to be planar. The relative energies, entropies,

dipole moments and the lowest frequencies are in Table 3.1.

Ox O O O, H \

anti-Z-1 syn-Z-1 anti-E-1 H

syn-E-1

The two anti conformations are calculated to be equal energy, although

the previous RHF/6-31G** optimization placed the E conformation 0.3

kcal/mol lower than the Z.^i The syn-Z-1 is located 2.0 kcal/mol higher in

energy than anti ones. The trends in energies are not simply explained by the

dipole moments. It has been suggested that a balance between electrostatic

and steric effects determine the conformational preference of substituted

ketenes.2a.i3,i4 The stability of anti-.E-l is definitely associated with its small

dipole moment. The stability of anti-Z-1 can be explained by the electrostatic

attraction between the nitrogen lone pair and the partially positive ketene

carbon. The net result is that the two conformers are of equal stability. The

46

syn-Z-1 is 2.0 kcal/mol higher than the anti ones due to the steric and

electrostatic repulsions between the hydrogen on nitrogen and the

electropositive ketene carbon.

Table 3.1 Relative Energies, Entropies, Dipole Moments and Low or Imaginary Frequencies of Structures Related to 1, Optimized at the MP2/6-31G** Level

MP2/6-31G** a

MP3/6-31G** a

MP4(SDQ)/6-31G** «

MP4a+ZPEb

S (caUmol-K)

MCDY

low freq (cm-i)

anti-Z-1

0.0

0.2

0.0

0.0

71.8

3.56

149.5

syn-Z-1

2.2

1.2

2.1

2.0

72.7

2.90

107.7

anti-E-1

0.2

0.0

0.0

0.0

71.4

1.23

132.7

syn--E-l

0.7

0.7

0.5

0.5

71.7

2.23

123.5

a Calculated using the frozen core approximation, in kcal/mol. ^ Zero-point vibrational energy correlation from MP2/6-31G** frequencies and scaled by 0.9646 (reference 10). ^ From the RHF/6-31G** electron distribution, at the MP2/6-31G** geometry.

The comparison of Mulliken charges between imidoylketene and

formylketene supports our anticipation that imidoylketene will have greater

basicity/nucleophilicity compared to formylketene (Figure 3.1).

47

0.205

y ^ 0.605 -0.368

Lo.201

H N .0.611 0.139

H 0.264

Relative energy

Dipole

Entropy

anti-Z-1

0.0

3.56

71.8

H 0.268

H 0.173

^ ^ ^ C 0645 | < ^ 4 9 6

UD.368

^ -0 .545

Z-2

0.0

4.00

70.8

0.414

H 0.221

-0.580

0.263

N

H

.0 -0.446

0.538 •0.297

0.162

H 0.140

anti-E-1

Relative energy

Dipole

Entropy

0.0

1.23

71.4

H 0.281

o -0.528

Q -0.424

-U 0.578

0.433

0.349

' ' 0 . 1 7 6

E-2

0.3

2.37

70.7

Figure 3.1. Mulliken charges, relative energies (kcal/mol), dipole moments (D), and entropies (cal/mol«K) of imidoylketene (MP2/6.31G** level) and formylketene (MP2/6-31G* level)

48

The charge on the nitrogen in anti-Z-1 (-0.636) is more negative

compared to -0.545 on oxygen in Z-2. A similar trend is found between

nitrogen (-0.580) in anti-£J-l and oxygen (-0.528) in E-2. On the other hand,

the ketene carbon (0.605) in anti-Z-1 is less electrophilic than that (0.645) in

Z-2; similarly 0.538 vs. 0.578 in anti-E-1 and E-2. Although the nitrogen is

more basic, the ketene carbon appears to be less electrophilic in

imidoylketene. This can be understood by the resonance structure

considerations shown in Figure 3.2. The relative importance of the resonance

structure B in Z-2 compared to B in anti-Z-1 results in the ketene carbon in

formylketene being more electrophilic. Based on this criterion, imidoylketene

would readily act as a nucleophile and would be less susceptible to

nucleophilic attack as compared to formylketene.

.0 y ^ o

anti-Z-1

.0 y ^ ^ . o

o

o B

Z-2

Figure 3.2. Resonance structures in anti-Z-1 and Z-2

49

The barrier for the in-plane isomerization of anti-Z-1 to syn-Z-1 is

calculated to be 29.5 kcal/mol. Under the flash vacuum pyrolysis (FVP)

condition, this barrier, although significant, would be surmountable.

The ketene and imine IR frequencies (scaled by 0.96012 and 0.9427,^0

respectively) for the conformations of 1 are discussed to aid the experimental

identification of imidoylketene and are shown in Table 3.2.

Table 3.2. Predicted Infrared Absorptions for Isomers of 1, at the MP2/6-31G** Level

Structure

anti-Z-1

syn-Z-1

anti-E-1

syn-E-1

5a

6a

C=Na

1586.4

1571.3

1594.3

1584.6

1684.4f

1656.2d

Intensity^

366.6

94.1

162.9

158.5

412.0

266.5

C=C=Oc

2139.6

2126.9

2133.7

2132.3

2150.6

2042.5e

Intensity^

552.4

515.3

643.4

642.5

1369.8

461.3

a In cm-1. Scaled by 0.9427 (reference 10). b km/mol. c In cm'l. Scaled by 0.960 (reference 13). d C=0 stretch, e C=C=N stretch. ^0=0 stretch.

50

Imidoylketene (1) was detected by IR spectroscopy by Wentrup et al.^^

The 2130 cm-i absorption peak observed is in the typical region of C=C=0 on

imidoylketene 14 and is assigned as 1. This is in good agreement with the

calculated peaks in 2139.6-2126.9 cm-i range (Table 3.2), even though the

various conformations of 1 have not been distinguished. Since the calculated

ketene stretches are so closely spaced to each other (12.7 cm-i apart), it will

be impossible to distinguish them in solution. The anti-Z-1 and anti-E-1 are

both expected to be observed in matrix because they are equally stable. The

syn-E-1 would be somewhat difficult to distinguish because the its C=N peak

is close to anti-Z-1 and its C=C=0 peak is close to anti-E-1. This syn-E-1 is

calculated only 0.5 kcal/mol higher that anti ones. However, the substituents

on nitrogen would destabilize the syn-E-1 due to steric crowding. The syn-Z-1

would be easily distinguished due to its lower frequencies. However, the

higher energy of this conformation makes it less likely to be observed.

3.4 Addition of Water to Imidoylketene

As was discussed in equations 2.1, 2.9 and 2.10 in Chapter II, the

enaminoester precursor eliminates alcohol and generates imidoylketene as

an reactive intermediate. To study this reaction mechanism theoretically, we

used water as a simplest form of an alcohol due to the computational cost

(eq 3.1). The relative energies, entropies, dipole moments and the lowest or

51

imaginary frequencies for the cycloaddition of water to imidoylketene are

illustrated in Table 3.3. The optimized structures are shown in Figure 3.3.

y O

anti-Z-1

O

J N' H

8

'H

.H O

NH2

3a

O

A H

O

NH:

3a'

(3.1)

Table 3.3. Relative Energies, Entropies, Dipole Moments and Low or Imaginary Frequencies for the Water Addition to anti-Z-1, Optimized at the MP2/6-31G** Level

MP2/6-31G** a

MP3/6-31G** a

MP4(SDQ)/6-31G**

MP4a+ZPEb

S (cal/mol«K)

/i(D)c

low freq (cm^)

anti-Z-1 + H2O

8.3

7.3

a 7.3

5.3

7

0.0

0.0

0.0

0.0

88.2

4.08

56.6

8

2.6

6.3

5.8

6.3

76.7

3.63

208.5i

3a

-33.1

-35.4

-33.3

-30.1

77.4

4.72

90.5

3a'

-36.5

-38.8

-36.5

-33.2

77.3

2.75

366.1

^ Calculated using the frozen core approximation. In kcal/mol. ^ Zero-point vibrational energy correlation from MP2/6-31G** frequencies and scaled by 0.9646 (reference 10). cprom the RHF/6-31G** electron distribution, at the MP2/6-31G** geometry.

52

The ground-state geometry of (Z)-3-amino-2-propenoic acid (3a) was

optimized in CI symmetry at the MP2/6-31G** level. This structure was

essentially planar, with the exception of the amine, which was slightly

pyramidalized. A search for the transition structure 8 was performed with

constrained C2-09 bond distances. At the RHF/3-21G level, there was no

calculated barrier for the addition of water to anti-Z-1. This is the same

result for the addition of water to for my Ike to no. 2b A concerted transition

structure with CI symmetry for the addition of water to anti-Z-1 was

successfully obtained at the RHF/6-31G* and MP2/6-31G** level,

respectively. It is unusual for the 3-2IG and 6-3IG* basis set to give such a

difference in potential energy surface at the RHF level, although again the

same trend was found for formylketene.2b

53

AR=0.559

N, 1.533 (J

( ; AR=0.526 N r 1.007

y

^

• W N . ^

8 3a

Asynchronicity = 0.033

Figure 3.3. Optimized geometries for the water addition to imidoylketene at the MP2/6-31G** level. Partial bonds are dotted lines. Side views are provided. Bond lengths are in angstrom. See text for the definition of asynchronicity.

The asynchronicity of the transition states often provides the insight

into the reactivity of the reacting species. Asynchronicity can be defined

either by bond lengths or by bond orders. We used the former. The bond

extension (AR) is first obtained by comparison the forming/breaking bond

54

lengths between the transition state and the product. The asynchronicity is

then the difference between those bond extensions (AR). The positive value of

asynchronicity means that the nitrogen attack to the hydrogen leads the

reaction. The Figure 3.4 shows the bond extensions and the asynchronicity

for the addition of water to imidoylketene and the comparison between the

formylketene ones.

O 1.943

jy \ " " [:j 1.533

8

AR=0.559

AR=0.526

^1.384

OH

H 1.007

3a Asynchronicity = 0.033

9 1.867

O 1.523

9

AR=0.481 O

A 1.386

AR=0.541 ^O'

3b

OH

•H

0.982

Asynchronicity = -0.060

Figure 3.4. Comparison between the calculated asynchronicities in the transition states of water addition to imidoylketene (MP2/6-31g** level) and formylketene (MP2/6-31G* level). Bond lengths are in angstroms. The leading bond extension (AR) is underlined. See text for the definition of asynchronicity.

55

The asynchronicity of the addition of water to imidoylketene is

calculated to be 0.033 A. The basicity of the nitrogen is leading the reaction of

anti-Z-1 to water and the nucleophilic attack of the water oxygen to the

ketene carbon follows. This indicates that the electron donating substituents

on the nitrogen would accelerate the addition reaction. The situation is

opposite with the formylketene. For the addition of water to the formylketene

(9), the asynchronicity is 0.060 A. The leading attack is the water oxygen

coming to the ketene carbon and the nucleophilic oxygen attack from the Z-2

to abstract the hydrogen from water lags (Figure 3.4). This opposite result

can be explained by considering that the nitrogen in imidoylketene is a better

base compared to oxygen in formylketene, which favors the N5-H9 bond

formation in the transition structure (8).

We note that the asynchronicity at the RHF/6-31G* level for the

reaction of imidoylketene with water is reversed from the result at the

MP2/6-31G** level. With RHF the nucleophihc attack of the water oxygen to

the anti-Z-1 was calculated more proceeded than the other bond formation. It

suggests that any interpretation based on the RHF level calculations has to

be considered with caution.

The transition state geometry (8) is calculated to be planar as expected

from the formylketene reaction with water (Figure 3.4). This is anticipated to

be common for a pseudopericyclic reaction.2.'7 As discussed earlier in the

56

previous chapter, the conventional pericyclic reactions have nonplanar

transition states to maximize the orbital overlap. In 8, except for the

spectator hydrogen on water which is being slightly out of plane, all the

participating atoms for the bond breaking or forming are in the same plane.

This planar transition state lacks the cyclic loop of interacting orbital

overlap, because there is little or no overlap between n (out-of-plane) and a

(in-plane) orbital systems in the transition structure. This results in an

orthogonality between n and a orbitals along the reaction coordinate. This

avoids the lack of electron-electron repulsions encountered in the cyclic

overlap; the barrier can be remarkably low as discussed below.

The energy of transition structure 3a is below that of the reactants

(anti-Z-1 plus water), 5.7 kcal/mol at the MP2/6-31G** level and 1.5 kcal/mol

at the MP4/6-31G** level, but 1.0 kcal/mol above at the MP4(SDQ) + ZPE

level, respectively. The requisite hydrogen bonded intermolecular complex of

reactants 7 was obtained as in the case of formylketene with water, which is

8.3 and 5.3 kcal/mol below the reactants energy at the MP2/6-31G** and

MP4(SDQ) + ZPE levels, respectively. The calculated activation barrier of 6.3

kcal/mol (MP4(SDQ)/6-31G**+ZPE level) is surprisingly simUar to the 6.5

kcaymol (MP4(SDQ)/6-31G*+ZPEi7 level) for the formylketene one. The

direct comparison is not appropriate due to the different basis set, however,

the barriers are undoubtedly close to each other. It is already mentioned that

57

the imidoylketene is more basic due to the nitrogen but less susceptible to the

electrophilic attack based on the charge comparison with the formylketene

(Figure 3.2). Overall, the activation barriers of the water additions to those

ketenes are appeared to be very close.

As was the case of the formylketene, the rotamer (3a') was found to be

3.1 kcal/mol lower than the initially formed conformation (3a). The barrier

from 3a' to form anti-Z-1 with the elimination of water is calculated to be

39.5 kcal/mol. This barrier is higher than that (30.9 kcal/mol computed at the

MP4(SDQ)/6-31G*//MP2/6-31G* + ZPE) for the loss of water from 3-

hydroxypropenoic acid (3b') to form formylketene (Z-2).2b These calculated

barriers agree that these ketenes are generated and observed experimentally

under the FVP or solution pyrolysis.

In both conformers of 3-aminopropenoic acid 3a and 3a', we notice that

the nitrogen (N5) is slightly pyramidalized. The dihedral angle of C3H4N5H8

is 164.0 0 in 3a and 169.0 ^in 3a'. Apparently, the conjugation with the

vinylogous system does not enforce the complete planarity in this case.

Although vinylogous amides are indeed planar in solid phase crystal

structures, 18 vinylogous carbamates have been observed to be slightly out-of-

plane. i The nitrogen in urea was optimized to be non-planar.20 It has been

suggested that pyramidalization of amides occurs in proteins.21

58

3.5 Addition of Formaldehyde to Imidovlketene

For the cycloaddition of imidoylketene and formaldehyde, the

geometries of the transition state 10 and the product 4a were successfully

located at both RHF/6-31G* and MP2/6-31G** levels (eq 3.2). The relative

energies, entropies, dipole moments and the lowest or imaginary frequencies

for the cycloaddition of formaldehyde to imidoylketene are reported in Table

3.4. The optimized structures are shown in Figure 3.5.

O

N

anti-Z-1

O II

CH2

O

J-N-H

O ;i

-CH-

10

o

N" H 4a

(3.2)

The concerted transition state 10 was located, but it is rather

asynchronous, with the N5-C9 bond 0.100 A more formed than the C2-O10

bond. The sense of asynchronicity (0.100 A) is increased compared to that

(0.033 A) of water addition to the imidoylketene. The oxygen is less

nucleophilic and the carbon less susceptible to the nucleophihc attack in

ketone than those in water. The greater asynchronicity in 10 means that the

nucleophilic attack from the nitrogen in imidoylketene is advanced in a

greater extent with formaldehyde than with water. Based on this

59

asynchronicity, we anticipate that the aldehydes should be more reactive

than ketones towards imidoylketenes.

AR=0.742

AR=0.642 N.I.435

T A ^ ^ ^ ^ ^ r

10 4a

Asynchronicity = 0.100

Figure 3.5. Optimized geometries for the formaldehyde addition to imidoylketene at the MP2/6-31G** level. Partial bonds are dotted lines. Side views are provided. Bond lengths are in angstroms. See text for the definition of asynchronicity.

60

The observed change in asynchronicity with imidoylketene from water

to formaldehyde was also detected with formylketene.2b The bond extensions

(formations) are both elongated by changing nucleophUe from water to

formaldehyde with formylketene. Interestingly, the extent of changes in the

bond extension along with the changing nucleophUe from water to

formaldehyde is greater with imidoylketene than formylketene. Based on this

observation, we suggest that imidoylketene would be more sensitive to the

nucleophiles for its addition reactions than the formylketene.

Table 3.4. The Effect of Changing NucleophUes to the Bond Extensions in the Transition State Geometries of Imidoylketene and Formylketene

bond extension^

C2-O10

N5-H9(C9)

bond extension^

C2-O10

05-H9(C9)

anti-Z-l+H20

0.559

0.526

Z-2+H2O

0.481

0.542

anti-Z-l+CH20

0.742

0.642

Z-2+CH2O

0.626

0.668

changeb

0.183

0.116

changeb

0.145

0.127

3 Bond distances are in angstroms. Bond extension is the difference in bond length between TS and product. Geometry parameters were optimized at the MP2/6-31G** level, b Difference in bond extension. This reflects the sensitivity of the corresponding bond to the nucleophUe.

61

The sign of asynchronicity in the formylketene reactions is opposite to

the imidoylketene ones (-0.042 vs.0.100 in Figure 3.6). The greater

nucleophilicity of the nitrogen and the decreasing electrophilicity of the

ketene carbon as an offspring convert the asynchronicity of imidoylketene

from that of formylketene. (For the resonance structures, see Figure 3.2.)

O 2.125 yz I I

H'2.077

10

AR=0.742

AR=0.642

O

yo 1.383

H' 1.453

Asynchronicity = 0.100 4a

O

J O

1.867

"^O I

y

1.523 11

AR=0.626 O

A 1.386 O

AR=0.668 ^O

4b

J 0.982

Asynchronicity = -0.042

Figure 3.6. Comparison between the calculated asynchronicities in the transition states of formaldehyde addition to imidoylketene (MP2/6-31G** level) and formylketene (MP2/6-31G* level). Bond lengths are in angstrom. The leading bond extension (AR) is underlined. See text for the definition of asynchronicity.

62

The activation barrier for the formaldehyde addition to anti-Z-1 is

calculated to be 10.6 kcal/mol (Table 3.5). Again, it is quite close to the 10.9

kcal/mol for the formaldehyde addition to the for my Ike to no. 2b Although we

are not aware of any experimental data to discuss with, this low barrier

suggests that the addition of ketones or aldehydes to imidoylketene is a very

plausible reaction.

Table 3.5. Relative Energies, Entropies. Dipole Moments and Low or Imaginar>^ Frequencies for the Formaldehyde Addition to anti-Z-1, Optimized at the MP2/6-31G** Level

MP2/6-31G** a

MP3/6-31G** a

MP4(SDQ)/6-31G** ^

MP4^+ZPEb

S (caUmoUK)

M(py low freq (cm-i)

anti-Z-l+CH20

0.0

0.0

0.0

0.0

10

3.7

8.8

8.0

10.6

82.5

4.50

331.li

4a

-45.0

-47.7

-43.1

-36.4

75.4

6.00

148.9

a Calculated using the frozen core approximation, In kcal/mol. ^ Zero-point vibrational energy correlation from MP2/6-31G** frequencies and scaled by 0.9646 (reference 10). ^From the RHF/6-31G** electron distribution, at the MP2/6-31G** geometry.

63

The 4.3 kcal/mol higher barrier and the 3.2 kcal/mol more exothermic

addition of formaldehyde to the imidoylketene is not explained simply by the

Hammond postulate (Figure3.7).22 The difference in exothermicity reflects

the thermodynamic properties of the molecules. Breaking the strong 0-H a-

bond to form 3a' is less favorable than breaking the C=0 Ti-bond to form 4a.

The higher barrier for the formaldehyde addition may be attributed by its

different electrophiUcity and nucleophihcity compared to water. Water being

more nucleophilic and more electrophilic compared to the formaldehyde

allows to have lower barrier for the reaction with the imidoylketene.

Relative Energy

(kcal/mol)

10.6

6.3

0.0

-33.2

•36.4

1 anti-Z-l+H20 anti-Z-l+CH20

4.3 kcal/mol

•f

4a

Figure 3.7. Energy diagram for the addition reactions of imidoylketene computed the MP2(FC)/6-3lG** level

64

The calculated difference in reactivity of imidoylketene towards water

and formaldehyde as nucleophiles should provide synthetically useful

selectivity of an imidoylketene with an alcohol in the presence of an aldehyde

or ketone. This also suggests that the trapping of imidoylketene from the

emanino ester precursor with a ketone is not practical because the

imidoylketene intermediate would react faster with the alcohol bj^^roduct

than with the ketone. An attempt was made to produce imidoylketene from

the pyrrole-2,3-dione as a precursor since the only byproduct is carbon

monoxide. This work is still in a progress.

3.6 Addition of Ammonia to Imidoylketene

Compared to water and formaldehyde, ammonia is anticipated to be

more reactive due to the greater nucleophilicity of the nitrogen. The previous

calculation for the reactivity of formylketene was performed only with water

and formaldehyde.2b To complete the theoretical study on the reactivity of

imidoylketene and formylketene, and also from the result of enhanced

experimental reaction rate for an amine addition compared to an alcohol in

our laboratory, 23 we undertook ab initio calculations on the addition of

ammonia to imidoylketene and formylketene (eq 3.3).

65

The geometries for the ammonia addition to imidoylketene were

optimized at the MP2/6-31G* level for the direct comparison with

formylketene. Relative energies and entropies are reported in Tables 3.6 and

3.7. The optimized geometries are shown in Figure 3.8.

Q NH'

W" H2N-H 0 7 \

NH / /

12 Complex

H2 N-.

Qv/ H

,NH

13

O NH2 H

NH

14

Q NH-

/ O

H2N-H O '

\ \ / o

/

15 Complex

H2 N

O '' ^^

16

O NH2 H

O

17

(3.3)

The tight molecular complexes (12 and 15) as true energy minima were

located as was the case of water with both ketenes. Both transition states (13

and 16) are completely planar as expected for the pseudopericycUc orbital

overlap. Those are late transition states with both C2-N7 and N5(05)-H6

almost completely formed.

66

The reaction barriers for both ketenes are calculated very low at the

MP level. With the zero-point energy (ZPE) correction, however, these small

energ}' gaps disappeared (-0.9 kcal/mol in both cases)! This rather extreme

result is in qualitative agreement with the experimental observation in that

much a faster reaction rate was detected for a-oxoketene with propylamine

than with l-butanol.23 Based on the barrier difference between the water

addition and ammonia addition to formylketene, however, much dramatic

selectivity should be observed experimentally. Although several factors make

the solution phase experiments different fr'om the gas phase calculations, the

quantitative comparison between the computational and experimental

barrier still remains for further study.

67

K 13

W ''•306

<

15 16

Figure 3.8. MP2/6-31G** optimized structures for the addition of imidoylketene (12 and 13) and formylketene (15 and 16) Partial bonds are unfilled. Side views are provided. Bond lengths are in angstroms.

68

Table 3.6. Relative Energies and Entropies of Minima and the Transition Structure in the Addition of Ammonia to Imidoylketene, at the MP2/6-31G* Optimized Geometry

level of theory

MP2/6-31G*«

MP3/6-31G*a

MP4(SDQ)/6-31G*^

MP4(SDQ)a + ZPEb.c

-TASb.e

anti-Z-1 + NH3

13.1

10.9

8.8

5.0

16.3

12

0.0

0.0

0.0

0.0

0.00

13

0.4

0.8

1.1

-0.9d

0.4

14

-23.6

-28.0

-27.2

-25.9

0.1

^ Energ}^ in kcal/mol ^ From the MP2/6-31G* frequency calculations. ^ Zero point energy scaled by 0.9646. ^ Note that the calculated energ}* of 13 is be low that of the complex 12. See text for further discussion. ^ At 110° C.

Table 3.7. Relative Energies and Entropies of Minima and the Transition Structure in the Addition of Ammonia to Formylketene, at the MP2/6-31G* Optimized Geometry

level of theory

MP2/6-31G*a

MP3/6-3lG*a

MP4(SDQ)/6-31G*a

MP4(SDQ)a+ZPEb.c

-TASb.e

formylketene + NH3

5.2

4.7

10.2

8.2

-16.4

15

0.0

0.0

0.0

0.0

0.00

16

0.8

0.6

1.1

-0.9d

0.4

17

-10.0

-15.5

-13.5

-12.6

0.3

a Energ>- in kcal/mol ^ From the MP2/6-31G* frequency calculations. ^ Zero point energy scaled by 0.9646. ^ Note that the calculated energy of 16 is be low that of the complex 15. See text for further discussion. ^ At 110° C.

69

3.7 1.3-Hvdrogen Shifts

1,3-Hydrogen shifts in hydrocarbons are orbital symmetry forbidden.

However, with a pseudopericyclic orbital topology, they are aUowed.25 From

the pyrolysis of the Meldrum's acid derivatives(18), (aminomethylene)ketene

(5a) has been matrix isolated and observed by IR spectroscopy (eq 3.4).i314.26

Q Q

A - ^ ^>' Jii^ 1 (3.4) -(CH3)2=0 NH ^ N -

^NH2 H 18 E-1 5a

To explain this observation, we undertook the theoretical computation

on the 1,3-hydrogen shifts of anti-E-1 to generate 3-amino-l,2-propadien-l-

one (5a) and oxoketenimine (6a) (eq 3.5 and 3.6). The relative energies,

entropies, dipole moments and the lowest or imaginary frequencies for the

1,3-shifts are shown in Table 3.8. The optimized structures are shown in

Figure 3.9.

70

HN

1 y> '•'-^-^

N ^ k

H N A ^ H

anti-£-1 19

H

anti-E-1

"• 'A 20

^ 0

H

v° HN^^^i^^ (3.6)

^

5a

H H (3.6)

6a 6a'

Table 3.8. Relative Energies, Entropies, Dipole Moments and Low or Imaginary Frequencies of Structures Related to 1. Optimized at the MP2/6-31G** Level

anti-E-1 19 oa 20 6a 6a'

MP2/6-31G**« 0.2

MP3/6-31G** a 0.0

MP4(SDQ)/6-3lG**« 0.0

MP4a+ZPEb 0.0

S (cal/moNK) 71.4

M(Dy 1.23

low freq (cm-i) 142.7

50.6

59.1

58.0

54.8

72.1

4.22

1940.1i

7.4

12.0

12.3

12.9

72.9

6.00

134.7

50.5

59.9

57.0

53.4

69.8

2.75

1047.1i

6.0

4.9

5.4

4.8

71.5

4.18

147.3

16.6

17.2

17.8

17.0

71.0

6.67

805.3i

^ Calculated using the frozen core approximation. In kcal/mol. ^ Zero-point vibrational energy correlation from MP2/6-31G** frequencies and scaled by 0.9646 (reference 10). ^From the RHF/6-31G** electron distribution, at the MP2/6-31G** geometry.

71

o.

- • " 1.441 1.337 H,

1 V

19

( )

5a

H e ,

1.469 #

O-

N«

1.368 -

y C2

A^3

"yy

20

I )

6a 6a'

Figure 3.9. MP2/6-31G** optimized structures related to 1,3-hydrogen shifts of 1. Partial bonds are dotted fines. Side views are provided. Bond lengths are in angstroms.

72

The methyleneketene (5a) was optimized to be planar but strongly

bent at C3, simUarly to the hydroxyl compound 5b.2e This bent geometry can

be understood from a resonance point of view (Figure 3.10). The in-plane

electron donation from the ketene oxygen increases the electron density of

C2. At the same time, the electron deficient ketene oxygen regains the

electron density from the nitrogen out-of-plane lone pair. The accumulated

electron density on C2 generates the rehybridization on this carbon. This

electronic effect results the bent geometry observed in our calculation.

„,V°- "H;A - ™ A H H Q H Q

Figure 3.10. Resonance structures of 5a

The transition state 19 was calculated to be planar, as was the

transition state from E-2 to 5b.2e The rearrangement of 5a to E-1 is

calculated to be less exothermic (12.9 kcal/mol) than that of 5b to E-2 (23. 8

kcal/mol at the MP4(SDQ)/D95**//MP2/6-3lG* + ZPE). This can be explained

by thermodynamics in that the formation of the C=0 in E-2 is more favorable

than that of the C=N in E-1. The rearrangement to E-1 has a higher barrier

73

(41.9 kcal/mol) than that of E-2 (33.1 kcal/mol) as in agreement with the

Hammond postulate.22 This barrier can be overcame in the FVP condition

(usually higher than 400 °C) for the thermolysis of the Meldrum's acid

derivatives.

The 1,3-hydrogen shift of E-1 to 6a has also been proposed by Wentrup

et a/.25b The structure of 6a is optimized as almost planar except for the

hydrogen on the nitrogen because the C=N Ti-bond is in the plane of the

molecule. However, in the transition state 20, this hydrogen is almost in the

same plane of the molecule as well as the transferring hydrogen. The barrier

for forming 6a from anti-E-1 is calculated fairly high (48.6 kcal/mol) (see

Figure 3.11). This is even higher than the barrier (33.8 kcal/mol) of the

degenerate rearrangement of E-2. The barrier of formylallene (6c) to form

vinylketene is the highest (54.9 kcal/mol) but the most exothermic.25b This

opposing trend, which is counter to the Hammond postulate22 can be

rationalized by the detailed analysis of the molecular orbital topology. The

orbital topology of 6b is completely pseudopericyclic. The hydrogen

transferred is in the plane of the molecule and this does not overlap with the

out-of-plane n orbitals. In 6a, the in-plane lone pair (p orbital) on the

nitrogen must be transferred to be out-of-plane n bond. This does not aUow

the full pseudopericyclic orbital overlap untU it reaches the transition state

where the nitrogen p orbital is in-plane of the molecule. The rearrangement

74

of 6c has the most difficult situation to allow the pseudopericyclic orbital

topology. The CH2 on one end has to break the C=C Ti-bond to permit the

pseudopericycUc overlap, which results the highest barrier. Wentrup has also

explained this trend in terms of HOMO-LUMO energies.25

HoC

Q

HoC

H

O

H

Barrier

48.6'

33.8'

54.9'

Exothermicity

4.8

0.0

10.3

Figure 3.11. Reaction barriers and exothermicities of 1,3-H shifts of conjugated ketenes in kcal/mol. ^ calculated at the MP4(SDQ)/6-31G**//MP2/6-31G*+ZPE level, b calculated at the MP4(SDQ)/D95**//MP2/6-31G*+ZPE level. ^ calculated at the QCISD(T)/6-311+G(2d,p)//MP2/6-31G*+ZPE level.

75

To analyze the barrier of the rearrangement of 6a in more detail, we

constrained the geometry to be planar and optimized the linear structure

(6a'). This is 12.2 kcal/mol higher in energy than 6a. Then the hypothetical

reaction from 6a' to anti-E-1 has the barrier of 36.4 kcal/mol and the

exothermicity of 17.0 kcal/mol. It is concluded that the contribution of the

planarity to the barrier in this rearrangement is quite significant.

3.8 Conclusions

All four conformations of imidoylketene were explored using ab initio

molecular orbital calculation. The two anti-conformations are more stable

than the two syn-conformations at the MP2/6-31G** level of theory. This is

explained by the balance between the overall dipole moments of the molecule

and the electrostatic interactions with the central carbon. Based on a

comparison of the Mulliken charges, it appears that the nitrogen in

imidoylketene is more basic/nucleophilic than the oxygen in formylketene.

However, the ketene carbon in imidoylketene is more electrophilic than that

in formylketene due to the greater resonance donation to this carbon.

Transition structures at the MP2/6-31G** level for the additions of

both water and formaldehyde to imidoylketene were optimized as concerted,

planar and pseudopericyclic, as expected from the formylketene ones. The

calculated asynchronicities of the cycloadditions reflect the greater basicity

76

and nucleophilicity of the nitrogen compared to the oxygen in formylketene.

The MP4(SDQ)/6-31G** activation barrier difference between water and

formaldehyde addition implies synthetically useful selectivity between

alcohols and carbonyl compounds.

The 1,3-hydrogen shifts of cummulene (5a) and ketene imine (6a) to

give imidoylketene were calculated to have higher barriers than

corresponding ones to formylketene. The higher barriers can be explained by

the effective geometry in the transition states to allow pseudopericyclic

orbital topology.

77

3.9 References

1. (a) Boeckman, R. K., Jr.; Pruitt, J. R. J. Am. Chem. Soc 1989, 111, 8286-8288. (b) Boeckman, R. C , Jr.; Weidner, C. H.; Perni, R. B.; Napier, J. J. J. Am. Chem. Soc 1989, 111, 8037-8039. (c) GammiU, R. B.; Judge, T. M.; Phillips, G.; Zhang, Q.; Sowell, C. G.; Cheney, B. V.; Mizsak, S. A.; Dolak, L. A.; Seest, E. P. J. Am. Chem. Soc 1994, 116, 12113-12114.

2. (a) Ham, S.; Birney, D. M. Tetrahedron Lett. 1994, 35, 8113-8116. (b) Birney, D. M.; Wagenseller, P. E. J. Am. Chem. Soc 1994, 116, 6262-6270. (c) Wagenseller, P. E.; Birney, D. M.; Roy, D. J. Org. Chem. 1995, 60, 2853-2859. (d) Ham, S.; Birney, D. M. J. Org. Chem. 1996, 61, 3962-3968. (e) Birney, D. M. J. Org. Chem. 1996, ^7,243. (f) Matsui, H.; Zuckerman, E. J.; Katagiri, N.; Sugihara, T.; Kaneko, C ; Ham, S.; Birney, D. M. J. Phys. Chem. A 1997, 101, 3936-3941. (g) Birney, D. M.; Ham, S.; Unruh, G. R. J. Am. Chem. Soc 1997, 119, 4509-4517. (h) Ham, S.; Birney, D. M. Tetrahedron Lett. 1997, 38, 5925-5928.

3. The notation [4+2] here means the number of participating atoms from each reactants and does not necessarily designate the number of electrons in the cycloaddition because there are no cyclic loop around the interacting orbitals allowing pseudopericyclic overlap.

4. TidweU, T. T. Ketenes; John Wiley & Sons: New York, 1995.

5. Zhao, D.-C; Allen, A. D.; TidweU, T. T. J. Am. Chem. Soc 1993, 115, 10097-10103.

6. Barton, D. H. R.; Chung, S. K ; Kwon, T. W. Tetrahedron Lett. 1996, 37, 3631-334.

7. Ross, J. A.; Seiders, R. P.; Lemal, D. M. J. Am. Chem. Soc 1976, 98,

4325-4327.

78

8. Frisch, M. J.; Trucks, G. W.; Head-Gordon, M.; GiU, P. M. W.; Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M. A.; Replogle, E. S.; Comports, R.; Andres, J. L.; Raghavachari, K.; Binkley, J. S.; Gonzalez, C; Martin, R. L.; Fox, D. J.; Defrees, D. J.; Baker, J.; Stewart, J. J. P.; Pople, J. A. Gaussian 92. Gaussian, Inc.: Pittsburgh PA, 1992.

9. (a) Houk, K. N.; Li, Y.; Evanseck, J. D. Angew. Chem. Int. Ed. Engl. 1992, 31, 682-708. (b) Houk, K. N.; Gonzalez, J.; Li, Y. Ace Chem. Res. 1995, 28, 81. (c) Jiao, H.; Schleyer, P. v. R. Angew. Chem., Int. Ed. Eng. 1995, 34, 334-337. (d) Jiao, H.; Schleyer, P. v. R. J. Am. Chem. Soc 1995, 117, 11529-11535.

10. Pople, J. A.; Scott, A. P.; Wong, M. W.; Radom, L. Isr. J. Chem. 1993, 33, 345.

11. Nguyen, M. T.; Ha, T.; More O'FerraU, R. A. J. Org. Chem. 1990, 55, 3251-3256.

12. Kappe, C. O.; Wong, M. W.; Wentrup, C. J. Org. Chem. 1995, 60, 1686-1695.

13. Wentrup, C; Briehl, H.; Lorencak, P.; Vogelbacher, U. J.; Winter, H.-W.; Maquestiau, A.; Flammang, R. J. Am. Chem. Soc 1988, 110, 1337-1343.

14. Briehl, H.; Lukosch, A.; Wentrup, C. J. Org. Chem. 1984, 49, 2772-2779.

15. Birney, D. M. J. Org. Chem. 1994, 59, 2557-2564.

16. (a) Wiberg, K. B.; Laidig, K. E. J. Am. Chem. Soc 1987, 109, 5935-5943. (b) Perrin, C. L.; Young, D. B. Tetrahedron Lett. 1995, 36, 7185-7188.

17. This data is from the reference 2b except the zero-point energy scaled by 0.9646.10

79

18. (a) Bernth, N.; Larson, E.; Larson, S. Tetrahedron 1981, 37, 2477-2484. (b) Goti, A.; Brandi, A.; Danza, G.; Guarna, A.; Donati, D.; DeSarlo, F. J. Chem. Soc, Perkin Trans. 119S9, 1253-1258. (c) Fernandez-G., J. N.; Enriquez, R. G.; Tobon-Cervantes, A.; Bernal-Uruchurtu, M. I.; Villena-I., R.; Reynolds, W. F.; Yang, J.-P. Can. J. Chem. 1993, 71, 358-363. (d) Bailey, N. A.; Fenton, D. E.; Gayda, S. E.; PhiUips, C. A. J. Chem. Soc, Dalton Trans. 1984, 2289-2292. (e) Bresciani-Pahor, N.; CaUigaris, U.; Nardin, B.; Randaccia, L.; Viterbo, D. Acta Cryst. 1979, B35, 2116-2118.

19. (a) HesUn, J. C ; Moody, C. J.: Slawin, A. M. Z.; WUUams, D. J. Tetrahedron Lett. 1986, 27, 1403. (b) Balogh, M.; Lazlo, P.; Simon, K. J. Org. Chem. 1987, 52, 2026. (c) Vainiotalo, P.: Savolainen, P.-L.; Ahlgren, M.; Malkonen, P. J.; Vepsalainen, J. J. Chem. Soc, Perkin Trans. 2 1991, 735.

20. Rasul, G.; Prakash, G. K. S.; Olah, G. A. J. Org. Chem. 1994, 59, 2552.

21. Sulzbach, H. M.; Scheleyer, P. v. R.; Schaefer, H. F., III. J. Am. Chem. Soc 1995, 117, 2632-2637.

22. Hammond, G. S. J. J. Am. Chem.Soc. 1955, 77, 334.

23. The experiment was performed by my coworker, XiaoUan Xu in our laboratory. This result was pubUshed in a paper.24

24. Birney, D. M.; Xu, X.; Ham, S.: Huang, X. J. Org. Chem. 1997, 62, 7114-

7120.

25. Wentrup et al. have reported the vinylketene-acylaUene rearrangement. (a) Bibas, H.; Wond, M. W.; Wentrup, C. Chem. Eur. J. 1997, 3, 237-248. (b) Wong, M. W.; Wentrup, C. J. Org. Chem. 1994, 59, 5279-5285. (c) Bibas, H.; Wong, M. W.; Wentrup, C. J. Am. Chem. Soc 1995, 117, 9582-9583. (d) Fulloon, B.; El-Nabi, H. A. A.; KoUenz, G.; Wentrup, C. Tetrahedron Lett. 1995, 36, 6547-6550. (e) FuUoon, B.; Wentrup, C. J. Org. Chem. 1996, 61, 1363-1368. (f) Koch, R.; Wong, M. W.; Wentrup. C. J. Org. Chem. 1996, 61, 6809. (g) Koch, R.; Wong, M. W.; Wentrup, C. J. Org. Chem. 1997, 62, 1908.

80

26. (a) Grandjean, D.; Dhimane, H.; Pommelet, J.-C; Chuche, J. Bull. Soc. Chim. Fr. 1989, 126, 657-660. (b) Cheikh, A. B.; Chuche, J.; Manisse, N.; Pommelet, J. C; Netsch, K.-P.; Lorencak, P.; Wentrup, C. J. Org. Chem. 1991, 56, 970-975. (c) Kappe, C. O.; Kollenz, G.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 487-490. (d) Chuburu, F.; Lacombe, S.; GuUouzo, G. P.; Wentrup, C. New. J. Chem. 1994, 18, 879-888. (e) Mosandl, T.; StadtmuUer, S.; Wong, M. W.; Wentrup, C. J. Phys. Chem. 1994, 98, 1080-1086.

81

CHAPTER IV

CHEMOSELECTIVITY IN THE REACTIONS

OF IMIDOYLKETENE

4.1 Introduction

Our predictions based on the ab initio calculations indicate that the

reactions of imidoylketene with nucleophiles would be facUe due to the low

barriers. 1 The very low barriers along with the planar transition states were

discussed in terms of the pseudopericyclic orbital topology in the previous

chapter.2-3 Despite the potentially useful synthetic applications of

acetimidoylketene (1), with the best of our knowledge, no systematic studies

of trends in the reactivities of this ketene have been reported.4

O, N'

\A

We therefore undertook the systematic study of competition reactions

of acetimidoylketene with various alcohols and cyclohexanone as nucleophiles

with two goals in mind. The first is to provide the reactivity information on

the imidoylketene. The second is to test the validity of our earlier predictions

regarding the pseudopericyclic planar transition states.

82

4.2 Competitive Reactions of Acetimidoylketene with Alcohols

Three precursors which have primarily been used to generate

acetimidoylketene were introduced in Chapter II. Previous work in our

laboratory was successful in generating acetylketene intermediate using a p-

keto ester (2a) as a precursor.^ This led us to the pyrolysis of ^butyl enamino

ester 3a for the generation of acetimidoylketene (1). Other enamino esters

have been shown to produce acetimidoylketene.^ The enamino ester 3 was

conveniently prepared by microwave irradiation of yS keto ester 2 and 1-

propylamine on silica gel (eq 4.1).'

O O H o N " " ^ - ^ / O HN

y^-j^ ysr~ yj'-^ <-> microwave

2a 3a

The competition reactions were carried out by refluxing 3a and the

excess amount of a desired alcohol in toluene. Authentic samples of the

products from the competition reactions were prepared either by thermolysis

of 3a with the desired alcohol (eq 4.2) or by microwave reaction of a f^keto

ester (2) with propylamine (eq 4.3). Acetylketene (5) is generated by

thermolysis of the versatUe precursor trimethyldioxinone (4) by thermolysis

and is trapped by the desired alcohols to form 2 (eq 4.3).

83

^ N ^ - ^ O HN'

3a ^ - ^ ° A A ^ ^ RoAA (4.2) -fBuOH

3 a R = -C(CH3)3 b R = -CH(CH3)2 C R = ~(CH2)3CH3 d R = -CH3 e R = -CH2CF3

r°XA ROH O O HoN'

•(CH3)2CO RO^^^"^ '^^^ microwave Si02

2 a R = -C(CH3)3 " - ^ b R = -CH(CH3)2 c R = -(CH2)3CH3 d R = -CH3 e R = -CH2CF3

The compound 3 are very sensitive to hydrolysis to give 2. This makes

the flash vacuum pyrolysis difficult. The competition reactions therefore were

performed by solution pyrolysis with the low conversion (less than 1%) to

minimize reverse reactions. The two alcohols used as nucleophiles to trap

acetimidoylketene were present in large excess so that the ratio of the

concentration between them stayed constant throughout the competition

analysis. The product ratio then reflects the kinetic reactivity/selectivity of

the two different trapping reagents. In this manner, the competition reaction

analysis was undertaken using various alcohols with aiming to achieve both

84

steric and electronic effects on the reactivity of acetimidoylketene towards

nucleophiles. The results are reported in Table 4.1.

Table 4.1. Results of Competitive Reactions of Pairs of Reagents with Acetimidoylketene (2) Generated by Pyrolysis of 3a in a Closed Vessel in Toluene Solution.^

O HN'

O + A+B P^C^3 , X+Y

A

3a

Reactants

A B

Mole ratio conv.b products

3a:A:B % X Y

mole ratio

X:Y

CH3(CH2)30H (CH3)2CHOH

CH3(CH2)30H CH3OH

CH3(CH2)30H CF3CH2OH

1:10:10 0.8%c 3c 3b

1:20:20 0.7%d 3c 3d

1:10:10 0.7%e 3c 3e

(25.1±0.8):1.0

1.0:(1.04±0.04)

(21.2±2.4):1.0

CH3(CH2)30H cyclohexanone l:0:solvent no reaction

^ Results are an average of three separate reactions. Product ratios were determined by GC, with the injector temperature 125 °C, oven temperature 80 °C, then 10 °/minute to 180 °C. ^ % conversion of starting material, c 2 hours at 128 °C. d 2 hours at 124° C. e 1 hour at 126° C.

85

From the results in Table 4.1, it is apparent that steric hindrance

leads to the observed selectivity in the nucleophilic additions of alcohols to

the acetimidoylketene. 2-Propanol reacts with acetimidoylketene much more

slowly than 1-butanol due to the steric crowding. The product mole ratio for

3c vs. 3b is 25.1: 1.0. This is even greater selectivity compared to the

observed one for the analogous competition reactions with acetylketene. The

product mole ratio between 1-butanol and 1-pentanol measured

experimentally is 3.0 : 1.0.8 jn a view of the transition state geometries

calculated by us, this increased selectivity for the acetimidoylketene is not

anticipated. In the gas phase transition structures optimized at the MP2

level, the 01-H8 distance is longer with the acetimidoylketene TS compared

to that in the acetylketene TS (Figure 4.1). On the other hand, based on the

comparison of changes in bond extensions discussed in the previous chapter,

imidoylketene is considered to be more sensitive towards the nucleophiles

than formylketene (see Table 3.4). Nevertheless, the observed results indicate

that the acetimidoylketene is more selective towards nucleophUes than

acetylketene in the solution phase.

86

2.695

\ 1.523

TS for imidoylketene+H20 TS for formylketene+H20

Figure 4.1. Transition states for the water additions with imidoylketene and formylketene optimized at the MP2/6-31G** and MP2/6-31G* level, respectively. Bond distances are in angstroms.

87

Since methanol and 1-butanol are both unhindered alcohols, they were

not expected to show large differences in their reactivity with

acetimidoylketene. Indeed, the measured product mole ratio (3c : 3d = 1.0 :

1.04) indicates tha t those two alcohols are equally reactive towards

acetimidoylketene. The same result was observed with acetylketene that

there was no selectivity between methanol and 1-propanol.'^

The competition reaction between 1-butanol and 2-methyl-2-propanol

could not be studied because the pyrolysis of the precursor 3a produces 2-

methyl-2-propanol. However, the competition reactions between 1 alcohol

and 3 » alcohol is available with ace ty Ike to no.8 The product mole ratio of the

competition reactions between 1-pentanol and 2-methyl-2-propanol as

nucleophiles to trap acetylketene is 8.2 : 1.0. This selectivity between 1°

alcohol and 3 ^ alcohol is greater than that (3.0 : 1.0) between 1° alcohol and 2

° alcohol. Such a steric discrimination of acetimidoylketene and acetylketene

is consistent with our earlier theoretical predictions that the nucleophilic

addition reactions of acetimidoylketene and acetylketene undergo via

concerted, planar and pseudopericyclic transition states.i'2a

From the theoretical investigations of these transition states, it is

anticipated tha t any changes on the acidity of the alcohol hydrogen as well as

the nucleophilicity of the alcohol oxygen would influence significantly

towards the reactivity of acetimidoylketene. To examine this effect.

88

trifluoroethanol (TFE) was used since the hydrogen is more acidic and the

oxygen is less nucleophihc than in a 1° alcohol. As shown in Table 4.1, 1-

butanol reacts 21.2 times faster than TFE does. Again, the acetimidoyUiotene

shows greater selectivity compared to acetylketene in the competition

reactions between TFE and 1° alcohol where 1-pentanol reacts 6.2 times

faster than TFE with acetylketene.8

4.3 Competitive Reactions of Acetimidoylketene with Ketones.

The ab initio molecular orbital calculations predict that ketones would

react much more slowly than alcohols with acetimidoylketene.i This was

indeed confirmed by our experiment. The pyrolysis of 3a with neat

cyclohexanone gave only the starting precursor under the same reaction

conditions which were successfuUy used to trap acetimidoylketene by other

reagents. Since we were able to trap the acetimidoylketene with other

nucleophUes under the same reaction conditions, it is reasonable to assume

that the intermediates 1 and 2-methyl-2-propanol were in fact formed from

the precursor (3a) and then underwent the reverse reaction to form the

starting material back. Apparently, although stericaUy hindered, 2-methyl-2-

propanol reacts with 1 much faster than does cyclohexanone. This

experiment suggests qualitatively that ketones indeed react much slower

89

with acetimidoylketene than alcohols as was predicted by our ab initio

calculations.

Since the enamino ester (3a) was not a practical precursor to

investigate the reactivity difference between ketones and alcohols, an

alternative precursor was synthesized (eq 4.4).

R

O

A

a R =

NH2 N

" X CH2CI2 R ^ ' ^

^ \ //

(COCI):

Et^N

b R = ^ / /

NO-

The li]r-pyrrole-2,3-dione 8 has been know for a long time^ and was

discussed as a precursor for the synthesis of imidoylketene in chapter II in

this dissertation. These heterocyclic diones are synthesized by

cyclocondensation of substituted imine 7 with oxalyl chloride, (COCl)2.io

However, our attempts to generate imidoylketene from 8 and trap it with

nucleophiles were not successful. We only obtained rearrangement products

90

(9) from the thermal pyrolysis and addition/ring opening products (10) from

photolysis (eq 4.5 and 4.6). Alternative approaches to give imidoylketene

intermediates are still in progress in our laboratory.

H O

H

Ph"^ N'

H

Ph'

O

H

N' H

(4.5)

hv

ROH

O H

R N-

10

o OR

H (4.6)

91

4.4 Conclusions

The relative reactivity of acetimidoylketene towards nucleophiles has

been reported for the first time and compared with that of acetylketene. The

kinetic analysis of the competition reactions of acetimidoylketene with two

different alcohols was performed to investigate the reactivity trends. The

results show that the acetimidoylketene has steric discrimination towards

alcohols, in order of steric preference MeOH ^ 1° > 2°. The acetimidoylketene

also shows the preferred reactivity towards alcohol compared to ketone. This

trend is very similar with the acetylketene reactivity. Acetimidoylketene

reacted remarkably slowly with TFE as compared to 1-butanol. This

indicates that changing nucleophilicity and/or electrophilicity of the reagents

affects the reaction rate of the acetimidoylketene. Although the reactivity

trends are similar between acetimidoylketene and acetylketene,

acetimidoylketene appears to be more selective than acetylketene towards

the addition reactions with nucleophiles.

The observed experimental selectivities are in good agreement with

our previous theoretical prediction based on the ab initio molecular orbital

calculation. This agreement between experiment and computation supports

the hypothesis that the addition reactions of acetimidoylketene with

nucleophiles occur via planar, pseudopericyclic transition states. The

92

observed steric and electronic selectivities of the acetimidoylketene suggest

further synthetically useful applications.

93

4.5 References

1. Ham, S.; Birney, D. M. J. Org. Chem. 1996, 61, 3962-3968.

2. (a) Birney, D. M.; Wagenseller, P. E. J. Am. Chem. Soc 1994, 116, 6262-6270. (b) Ham, S.; Birney, D. M. Tetrahedron Lett. 1994, 35, 8113-8116. (c) Wagenseller, P. E.; Birney, D. M.; Roy, D. J. Org. Chem. 1995, 60, 2853-2859. (d) Birney, D. M. J. Org. Chem. 1996, ^i ,243. (e) Matsui, H.; Zuckerman, E. J.; Katagiri, N.; Kaneko, C ; Ham, S.; Birney, D. M. J. Phys. Chem. A 1997, 101, 3936-3941. (f) Birney, D. M.; Ham, S.; Unruh, G. R. J. Am. Chem. Soc 1997, 119, 4509-4517. (g) Ham, S.; Birney, D. M. Tetrahedron Lett. 1997, 38, 5925-5928. (h) Birney, D. M.; Xu, X.; Ham, S. J. Org. Chem. 1997, 62, 7114-7120.

3. Ross, J. A.; Seiders, R. P.; Lemal, D. M. J. Am. Chem. Soc 1976, 98, 4325-4327.

4. (a) Maujean, A.; Marcy, G.; Chuche, J. Tetrahedron Lett. 1980, 21, 519-522. (b) Nguyen, M. T.; Ha, T.; More O'FerraU, R. A. J. Org. Chem. 1990, 55, 3251-3256. (c) Kappe, C. O.; Kollenz, G.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 487-490. (d) Kappe, C. O.; Kollenz, G.; Netsch, K.-P.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 488-490. (e) Clarke, D.; Mares, R. W.; McNab, H. J. Chem. Soc, Chem. Commun. 1993, 1026-1027. (f) Chuburu, F.; Lacombe, S.; GuUouzo, G. P.; Wentrup, C. New. J. Chem. 1994, 18, 879-888. (g) Fulloon, B.; El-Nabi, H. A. A.; Kollenz, G.; Wentrup, C. Tetrahedron Lett. 1995, 36, 6547-6550. (h) Wolf, R.; Wong, M. W.; Kennard, C. H. L.; Wentrup, C. J. Am. Chem. Soc 1995, 117, 6789-6790. (i) Fulloon, B. E.; Wentrup, C. J. Org. Chem. 1996, 61, 1363-1368. (j) Ham, S.; Birney, D. M. J. Org. Chem. 1996, 61, 3962-3968.

5. Huang, X. Thesis, Texas Tech University, 1994.

6. Moussounga, J. E.; Bouquant, J.; Chuche, J. J. Bull. Soc Chim. Fr. 1995, 132, 249-257.

7. Rechsteiner, B.; Texier-BouUet, J.; Hamelin, J. Tetrahedron Lett. 1993, 34, 5071-5074.

94

8. The experiment was performed by my coworker, Xiaolian Xu in our laboratory. This result was published in a paper.^

9. Birney, D. M.; Xu, X.; Ham, S.; Huang, X. J. Org. Chem. 1997, 62, 7114-7120.

lO.Mumm, O.; Munchmeyer, G. Ber. Dtsch. Chem. Ges. 1910, 43, 3345-3358.

11. Kappe, C. O.; Terpetschnig, E.; Penn, G.; Kollenz, G.; Peters, K.; Peters, E.-M.; Schnering, H. G. v. Liebigs Ann. 1995, 537-543.

95

CHAPTER V

EXPERIMENTAL

5.1 General Method

All commercially available reagents were used as supplied, unless

mentioned. Trapping reagents and solvents were distilled prior to use. 1-

Butanol was dried with MgS04 and distilled from Mg under N2. Methanol

was fractionally distilled from Mg. 2-Methyl-2-propanol was distilled from

CaO. 1-Propylamine was distilled from Zn powder at reduced pressure under

N2. Toluene was distilled from CaH2 under N2. All the solvents for the flash

column chromatography were distilled prior to use due to the possibility of

hydration of the products.

Authentic materials were prepared by solution pyrolysis. The crude

pyrolysate was purified by flash column chromatography on silica gel.

Aldrich mesh 60 A silica gel was used after being dried overnight in the oven.

Thin layer chromatography was performed on Whatman silica gel sheets. ^H

and l^C NMR spectra were consistent with the desired structures. Elemental

analyses were performed by Desert Analytics and were satisfactory for all

compounds.

NMR spectra were recorded in CDCI3 using either an IBM AF-200 (300

for proton and 75.47 MHz for carbon) or an IBM AF-300 (300 MHz for proton

96

and 75.47 TvIHz for carbon) instrument. AU spectra for the authentic

materials are Usted in the appendix where peak positions are given in ppm

(6) from internal tetramethylsUane and couphng constants (J) are reported in

Hertz (Hz).

Gas chromatographic (GC) analyses were carried out on a Hewlett-

Packard 5890A with a flame ionization detector, using a 30 m x 0.53 mm x

0.88 mm film thickness HP-1 (crosshnked methyl sihcone gum) and/or HP-5

(crosslinked phenyl methyl siUcon) column. Typical GC conditions were as

foUows: injector 125 °C, oven temperature 80 °C, then 10 °/min to 180°C. The

injector temperature was set as low as possible to avoid decomposition. GC

response factors were determined using mixtures of known concentrations.

5.2 Solution Pvrolyses

For the competition experiments, ^butyl X-propyl-3-amino-2-

butenoate (3a) and trapping reagent(s) were placed in a thick-walled glass

tube. This was fiUed with sufficient toluene so that there was minimal dead

space left on the top. The tube was flushed with nitrogen and sealed with a

Teflon "Ace-thread" plug. \Mien large dead space was left on the top,

inconsistent results were obtained because of the different vaporization rates

of reagents upon heating. The tube was then heated in an oU bath, behind a

blast shield. CAUTION: There is a risk of explosion when heating closed

97

glass containers. After heating for the time and at the temperature reported

in the following section, the pyrolysate were removed from the tube with a

smaU amount of ether and analyzed by GC, with correction for response

factors. The reported results are at least the average of three separate

experiments.

For the synthesis of the authentic samples, the precursors (3a or 2)

were placed in a tube with alcohol traps and toluene solvent. After heating in

an oil bath and cooling to room temperature, the excess solvent and/or

trapping reagents were removed by rotary evaporation. The residue was then

subjected to flash column chromatogi'aphy on siUca gel for the purification.

5.3 GC Analysis

GC Chromatography is a powerful technique for the compound

analyses both qualitatively and quantitatively. The qualitative analysis is

based on the fact that different compounds generally sustain different

retention times. The quantitative analysis is closely related to detectors. Five

different methods have been developed: area normalization, area

normaUzation with response factors, external standard, internal standard,

and standard addition, i

We used the area normalization with response factors. To obtain the

correction factors or relative response factors RF, two compounds are mixed in

98

ether with known molar ratio. The mixture were then injected into the GC.

The areas of the two peaks (Axi and Ax2) were then measured by a Hewlett

Packard 3392 A integrator. The response factor RF was calculated by the

equation 4.1 where Nxi is the mole of a compound XI and Nx2 is the mole of a

compound X2.

RF = (Axi / Ax2) / (Nxi / Nx2) (4.1)

Using the equation 4.1, RF was calculated for the product pairs of each

competitions.

For the measurement of the product mole ratio of the competition

reactions, the peak ratio of the pyrolysate (Kl and X2) was detected by GC.

Now, Axi / Ax2 and RF are known. Thus, Nxi / Nx2 are calculated by the

equation 4.2.

(Nxi / Nx2) = (Axi / Ax2) / RF (4.2)

The RF values used for the GC analysis were the mean of three

repetitions of each GC experiments. For the quantitative analysis of the GC

results, the above method was used to calculated the product mole ratio from

the peak ratio. This is needed because the peak ratio of products does not

99

directly represent the mole ratio due to the different heats of combustion of

the products. The GC conditions were always set the same throughout the

whole experiments, since the sensitivity of the detector vary at different

conditions.

5.4 Competition Reactions

5.4.1 Competitive Reactions of Imidoylketene with 1-Butanol and 2-jMethyl-2-propanol

The reactant mixture contained 0.20 g of ^butyl N-propyl-3-amino-2-

butenoate (3a) (1 mmol), 0.74 g of 1-butanol (10 mmol) and 0.60 g of 2-

methyl-2-propanol (10 mmol). These were placed with toluene as a solvent in

a thick-walled glass tube. After heating for 2 hours at 128 ^C, the mixture

was cooled to room temperature. The pyrolysate was then taken out from the

tube and was mixed with ether. This mixture was injected into the GC. The

GC conditions are listed in the previous section. The GC diagram showed the

formation of two desired products; zi-butyl N-propyl-3-amino-2-butenoate (3c)

and i-propyl N-propyl-3-amino-2-butenoate (3b) and large amount of

unreacted start ing materials identified by comparison to authentic materials.

The average % conversions from the starting materials were 0.8 %. The mean

peak ratio of two products (3c : 3b) was (11.24 ± 0.36) : 1.00. The mean

response factors RF was 0.448. From the equation 4.2, the calculated mole

ratio between two products was obtained as (25.1 ± 0.8) : 1.00.

100

5.4.2 Competitive Reactions of Imidoylketene with 1-Butanol and Methanol

The reactant mixture contained 0.10 g of ^butyl N-propyl-3-amino-2-

butenoate (3a) (0.5 mmol), 0.74 g of 1-butanol (10 mmol) and 0.32 g of

methanol (10 mmol). These were placed with toluene as a solvent in a thick-

walled glass tube. After heating for 2 hours at 124 ^C, the mixture was cooled

to room temperature. The pyrolysate was then taken out from the tube and

was mixed with ether. This mixture was injected into the GC. The GC

diagram showed the formations of two desired products; n-butyl N-propyl-3-

amino-2-butenoate (3c) and methyl N-propyl-3-amino-2-butenoate (3d) and

large amount of unreacted starting materials. The average % conversions

from the start ing materials were 0.7 %. The mean peak ratio of two products

(3c : 3d) was 1.00 : (1.58 ± 0.06). The mean response factors RF was 1.515.

From the equation 4.2, the calculated mole ratio between two products was

obtained 1.00 : (1.04 + 0.04).

5.4.3 Competitive Reactions of Imidoylketene with 1-Butanol and 2,2.2-Trifluoroethanol

The reactant mixture contained 0.20 g of ^butyl N-propyl-3-amino-2-

butenoate (3a) (1 mmol), 0.74 g of 1-butanol (10 mmol) and 1.00 g of

trifluoroethanol (10 mmol). These were placed with toluene as a solvent in a

thick-walled glass tube. After heating for 1 hour at 126 ^C, the mixture was

101

cooled to room temperature. The p\Tolysate was then taken out from the tube

and was mixed with ether. This mixture was injected into the GC. The GC

diagram showed the formations of two desired products: /i-butyl X-propyl-3-

amino-2-butenoate (3c) and trifluoroethyl X-propyl-3-amino-2-butenoate (3e)

and large amount of unreacted starting materials. The average % conversions

from the starting materials were 0.7 %. The mean peak ratio of two products

(3c : 3e) was (10.91 ± 1.25) : 1.00. The mean response factors RF was 0.515.

From the equation 4.2, the calculated mole ratio between two products was

obtained as (21.2 ± 2.4) : 1.00.

5.5 Syntheses of Authentic Materials

5.5.1 S\Tithesis of 3-Oxo-2-butenoic acid, buts'l ester (2c)

Dioxinone (4. 1.42 g, 10.0 mmol) and 1-butanol (2.22 g, 30.0 mmol) was

placed in a thick-waUed glass tube with toluene solvent. A mixture was

heated at 130 °C overnight. The excess 1-butanol. acetone by product and

solvent were removed b}' rotaiy evaporation. The purification of the product

was carried out b}' flash column chromatography on siUca gel. The eluent wa:

hexane/eth3'l acetate (95/5). A slight yeUow oU was obtained after removing

solvent. The purity of the product was confirmed by TLC. X^IR and

elemental analysis.

It was proposed that the Z-enol (2') is the initial product^ from the

102

hydration both in solution4 and in matrix isolation^ experiments as well as

supported by ab initio calculations^'^. (eq 5.3)

^ ^ ^ H2O

y^Q k = 1.5x10^8"''

0,

>

> /

-OH

-OH

2'

0^ ^ O H

= 0

2 (5.3)

The enol tautomer (2c') was observed in the product analysis by NMR

and GC.

IH NMR 5 0.89 (t, J= 7.3 Hz, 3 H), 1.33 (m, 2H), 1.60 (m, 2H), 2.24 (s,

3H), 3.42 (s, 2H), 4.09 (t, J = 6.7 Hz, 2H); 13C NMR 6 13.60, 18.98, 30.10,

30.42, 50.08, 65.23, 167.16, 200.63. Enol tautomer (partial spectrum, 2c') ^H

NMR 6 1.92 (s, 3H), 4.08 (t, IH, J= 6.7 Hz), 4.94 (s, IH), 12.08 (s, IH); ' 'C

NMR d 21.1, 30.6, 63.7, 89.7, 172.5, 175.2. GC peak ratio 1:1.9; 2c:2c' 11.4:1

by IH NMR.

Anal. Calculated for CSHHOS: C, 60.74; H, 8.92. Found: C, 60.57; H,

8.92.

103

The structures of 2c and 2c' are:

0 0 O OH

5.5.2 Synthesis of 3-Propylamino-2-butenoic acid. 1,1-dimethylethyl ester (3a)

1,1-Dimethylethyl 3-oxopropenonate (2a, 2.02g, 0.013 m) and 1-

propylamine (0.76g, 0.013m) was placed on silica gel (2g) in an open beaker

and irradiated in a commercial microwave oven for 2 minutes.^ The product

was removed from the silica gel by filtering, using hexane/ethyl acetate

(90:10) as the wash solvent. After concentration, the product was subjected to

flash chromatography (hexane/ethyl acetate (95:5) on silica gel). The purity of

the product was confirmed by TLC, NMR and elemental analysis.

IH NMR 6 0.93 (t, J= 8.6 Hz, 3 H), 1.44 (s, 9H), 1.54 (m, 2H), 1.86 (s,

3H), 3.11 (pseudo q, 2 H), 4.43 (s, IH) 8.46 (br s, IH); l^c NMR 5 11.43,

19.34, 23.78, 28.67, 44.74, 51.51, 83.38, 161.27, 172.00. A smaU amount of

the imine tautomer was also observed in the spectra. Partial spectrum of ^H

NMR 6 2.20 (s, 3H), 4.54 (s, 2H); l^c NMR 6 27.9, 30.5, 82.0. 3a:imine

tautomer = 25:1 by IH NMR.

Anal. Calculated for C11H21NO2: C, 66.30; H, 10.62; N, 7.03. Found: C,

104

66.37; H, 10.60; N, 6.70.

The structure of 3a is:

O HN'

^O' 3a

5.5.3 Synthesis of 3-Propylamino-2-butenoic acid, 1-methylethyl ester (3b)

A mixture of 0.20 g of ^butyl N-propyl-3-amino-2-butenoate (3a) (1

mmol) and 6.01 g of 2-propanol (0.1 mol) as a trapping reagent as well as a

solvent were placed in a think-walled glass tube with a stirrer. After being

flushed with N2, the tube was sealed a Teflon Ace-thread plug. The tube was

heated in an oil bath at 135 °C for two days until the reaction was complete.

The excess alcohol solvent was removed by rotary evaporation. The residue

was then purified using flash column chromatography. The eluent used here

was hexane : ethyl acetate (95 : 5). After removing the eluent solvents, a light

yellow oil was obtained. The purity of the product was confirmed by TLC,

NMR and elemental analysis.

IH NMR 5 0.94 (t, J = 7.4 Hz, 3 H), 1.19 (d, J = 6.2 Hz, 6 H), 1.54 (m.

105

2H), 1.86 (s, 3H), 3.13 (pseudo q, 2H), 4.37 (s, IH), 4.95 (septet, J = 6.2 Hz, 1

H), 8.55 (br s, IH); 13c NMR 6 11.36, 19.34, 22.22, 28.64, 44.71, 64.90, 82.19,

161.81, 170.23.

Anal. Calculated for C10H19NO2: C, 64.83; H, 10.34; N, 7.56. Found: C,

64.73; H, 10.57; N, 7.44.

The structure of 3b is:

O HN'

3b

5.5.4 Synthesis of 3-Propylamino-2-butenoic acid, 1-butyl ester (3c)

A mixture of 0.20 g of ^butyl N-propyl-3-amino-2-butenoate (3a) (1

mmol) and 3.7 g of 1-butanol (0.05 mol) as a trapping reagent as well as a

solvent were placed in a think-walled glass tube with a stirrer. After being

flushed with N2, the tube was sealed a Teflon Ace-thread plug. The tube was

heated in an oil bath at 135 ^C for two days until the reaction was complete.

The excess alcohol solvent was removed by rotary evaporation. The residue

was then purified using flash column chromatography. The eluent used here

was hexane : ethyl acetate (95 : 5). After removing the eluent solvents, a light

106

yellow oU was obtained. The purity of the product was confirmed by TLC,

NMR and elemental analysis.

IH NMR 6 0.89 (m, 6 H), 1.32 (m, 2H), 1.55 (m, 4H), 1.85 (s, 3H), 3.10

(pseudo q, 2H), 3.95 (t, 2H), 4.37 (s, IH), 8.52 (br s, IH); 13c NMR 6 11.26,

13.68, 19.15, 19.26, 23.54, 31.04, 44.61, 62.11, 81.61, 161.81, 170.67.

Anal. Calculated for C11H21NO2: C, 66.30; H, 10.62; N, 7.03. Found: C,

66.58; H, 10.80; N, 6.77.

The structure of 3c is:

3c

5.5.5 Synthesis of 3-Propylamino-2-butenoic acid, methyl ester (3d)

A mixture of 0.20 g of ^butyl N-propyl-3-amino-2-butenoate (3a) (1

mmol) and 6.4 g of methanol (0.2 mol) as a trapping reagent as weU as a

solvent were placed in a think-walled glass tube with a stirrer. After being

flushed with N2, the tube was sealed a Teflon Ace-thread plug. The tube was

heated in an oU bath at 135 oC for overnight until the reaction was complete.

The excess alcohol solvent was removed by rotary evaporation. The residue

107

was then purified using flash column chromatography. The eluent used here

was hexane : ethyl acetate (95 : 5). After removing the eluent solvents, a light

yellow oil was obtained. The purity of the product was confirmed by TLC,

NMR and elemental analysis.

IH NMR 5 0.93 (t, J= lA Hz, 3 H), 1.54 (m, 2H), 1.88 (s, 3H), 3.13

(pseudo q, 2H), 3.58 (s, 3H), 4.39 (s, IH), 8.53 (br s, IH); 13C NMR 5 11.31,

19.33, 23.60, 44.70, 49.82, 81.29, 162.07, 170.93.

Anal. Calculated for C8H15NO2: C, 61.12; H, 9.62; N, 8.91. Found: C,

61.03; H, 9.74; N, 8.64.

The structure of 3d is:

O HN'

H3CO' 3d

5.5.6 Synthesis of 3-Propylamino-2-butenoic acid, trifluoroethyl ester (3e)

A mixture of 0.20 g of ^butyl N-propyl-3-amino-2-butenoate (3a) (1

mmol) and 5.0 g of trifluoroethanol (0.05 mol) as a trapping reagent as well

as a solvent were placed in a think-walled glass tube with a stirrer. After

being flushed with N2, the tube was sealed a Teflon Ace-thread plug. The

108

tube was heated in an oil bath at 135 ^C for three days until the reaction was

complete. The excess alcohol solvent was removed by rotary evaporation. The

residue was then purified using flash column chromatography. The eluent

used here was hexane : ethyl acetate (95 : 5). After removing the eluent

solvents, a yellow oil was obtained. The purity of the product was confirmed

by TLC, NMR and elemental analysis.

IH NMR 5 0.95 (t, J = 7.2 Hz, 3H), 1.59 (m, 2H), 1.92 (s, 3H), 3.17

(pseudo q, 2H), 4.40 (q, J = 8.7 Hz, 2H), 4.48 (s, IH), 8.49 (br s, IH); 13C NMR

6 11.28, 19.42, 23.49, 44.86, 58.56 (q, J = 10.4 Hz), 80.00, 123.63 (q, J = 138.8

Hz), 163.93, 168.08.

Anal. Calculated for C9H14NO2F: C, 48.00; H, 6.27; N, 6.22. Found: C,

48.14; H, 6.39; N, 6.19.

The structure of 3e is:

O HN'

FsC^^O^ 3e

109

5.6 Synthesis of a Pyrroledione as an Alternative Precursor

5.6.1 Synthesis of A^-Propvl imine (7b)

p-Nitroacetophenone (1.12 g, 6.78 mmol) and propyl amine (0.42 g,

7.10 mmol) were placed in a 100 ml round bottom flask with 20 ml of freshly

o

distilled CH2CI2 and dried molecular sieves (4 A). The reaction mixture was

stirred at room temperature under N2 for overnight. The reaction was over 95

% complete by NMR. The product after the removal of the solvent by rotary

evaporation was used without further purification. The yield was 94 %.

IH NMR 6 1.00 (t, J= 7.3 Hz, 3H), 1.76 (m, 2H), 2.25 (s, 3H), 3.44

(pseudo q, 2H), 7.91 (d of d of d, J = 8.9, 9.3, 4.4 Hz, 2H), 8.20 (d of d of d, J =

8.9, 9.3, 4.4 Hz, 2H); 13C NMR 5 12.15, 15.56, 24.02, 54.39, 123.63, 127.45,

146.86, 148.24, 162.98.

The structure of 7b is:

N

OoN'

7b

110

5.6.2 Synthesis of N-Propyl l/j"-pyiTole-2.3-dione (8b)

In a 100 ml three-neck round bottom flask, oxalyl chloride (0.94 g, 7.4

mmol) and 18 ml of freshly distilled CH2CI2 was placed with a condenser in

the middle neck under N2, an addition funnel on one side neck and a

thermometer on the other neck. This was placed in a dry-ice acetone bath

(-78 oC). iV-Propyl imine 7b (1.29 g, 6.30 mmol) with 10 ml of distilled CH2CI2

were added into the addition funnel, then added into the reactants mixture

dropwise slowly for one hour. The color was turned from light yellow to

yellow upon addition. The addition funnel was rinsed with 5 ml of distilled

CH2CI2. Then it was filled with triethylamine (1.27 g, 12.5 mmol) and 10 ml

of distilled CH2CI2. This was added into the reactant mixture slowly for an

hour, The color was changed from yellow to dark yellow. The reaction flask

was warmed up to room temperature. The extraction was performed with

NaHCOa/brine and diethyl ether, followed by filtration with MgS04. After the

solvent removal, the red solid product was crystallized in the refrigerator.

The pure product was confirmed by NMR and TLC with 83 % yield.

IH NMR 6 0.77 (t, J = 7.4 Hz, 3H), 1.40 (m, 2H), 3.54 (t, J = 6.4 Hz,

2H), 5.53 (s, IH), 7.71 (d of d of d, J = 8.9, 9.1, 4.3 Hz, 2H), 8.41 (d of d of d, J

= 8.9, 9.1, 4.3 Hz, 2H); 13C NMR 6 11.01, 22.27, 43.08, 101.91, 124.50, 128.54,

135.39, 149.64, 158.92, 170.27, 182.98.

I l l

The X-ray crystal structure8 of this red crystal was determined to

elucidate the conformational feature of the substituted pyrroledione. The X-

ray structure with its geometrical parameters and LA spectrum can be found

in Appendix A.

The structure of 8b is:

O9N

8b

112

5.7 References

1. Miller, J. M.; Chromatography: Concepts and Contrasts, Wiley, New York, 1988.

2. Rechsteiner, B.; Texier-Boullet, J.; Hamelin, J. Tetrahedron Lett. 1993, 34, 5071-5074.

3. Chiang, Y.; Guo, H.-X.; Kresge, A. J.; Tee, O. S. J. Am. Chem. Soc 1996, 118, 3386-3391.

4. (a) Meier, H.; Wengenroth, H.; Lauer, W.; Vogt, W. Chem. Ber. 1988, 121, 1643-1646. (b) Buss, M.; Mayer, A.; Muller, K ; Meier, H. Liebigs Ann. 1996, 1223-1229.

5. Freiermuth, B.; Wentrup, C. J. Org. Chem. 1991, 56, 2286-2289.

6. Birney, D. M.; WagenseUer, P. E. J. Am. Chem. Soc 1994, 116, 6262-6270.

7. Allen, A. D.; McAllister, M. A.; TidweU, T. T. Tetrahedron Lett. 1993, 34, 1095-1098.

8. X ray crystallography was taken by Professor Bruce \Miittelsey in the Chemistry Department at Texas Tech University.

113

PART TWO

AB INITIO STUDIES OF THE REACTIVITY

OF NITROSOKETENE

114

CHAPTER M

BACKGROUND

Although ketenes have been studied for a long time and have been the

subject of numerous papers, i neither the reactions of the nitrosoketene

intermediate nor the detection of this reactive intermediate by spectroscopy

has been reported in the Uterature untU quite recently. In 1994, Katagiri et

al. first proposed nitrosoketene (2) as a reactive intermediate for the

synthesis of cychc nitrones (3) from the thermolysis of isonitroso Meldrum's

acid (1) in the presence of various ketones (eq 6.1).2 The synthesized nitrones

undergo 1,3-dipolar cycloaddition with electron-rich olefins to form the

corresponding isoxazolodine derivatives stereoselectively, which were

subsequently converted to amino acids.^

A

-CO 2,

O Ri -(CH3)2CO _ cr N

O

(6.1)

115

This new synthesis of cycUc nitrones (3) was considered to involve the

cycloaddition of ketones with the intermediate nitrosoketene (2) formed from

the isonitroso Meldrum's acid.- ^ Two pathways were suggested for the

formation of 3; (a) direct [3+2] cycloaddition of the E-conformer of 2 to give 3.

or (b) initial [4+2] cycloaddition of the Z-conformer of 2 to give dioxazinones

(4) foUowed by 1,2-rearrangement (eq 6.2).

.0 O

O'-' Ri''''^R2 cycloaddition N— '' 2

<^ 3 " '

1,2-mig ration

f + X ' " ' . r o % Ri R2 cycloaddition N ^^^^2

Ri ^•2 4 (6.2)

Katagiri et al. suggested that the reaction proceed by the [4+2]

pathway based on the HOMO and LUMO interaction between the ketone and

the Ti-system of 2.2b We have performed the RHF/6-31G* ab initio calculations

that the direct, pseudopericycUc [3+2] cycloaddition of E-2 to formaldehyde is

favored over the indirect [4+2] cycloaddition of Z-2 to formaldehyde foUowed

116

by a l,2-migration.4 However, the calculated asynchronicity of the [3+2]

transition state, where C-N bond formation leads the reaction and C-0 bond

foUows. are not in agreement with the experimental observations. Katagiri et

al. 2b pointed out that if the N-C bond leads the reaction, as the results of the

RHF calculations4 indicate, electron-withdrawing para-substituents on

acetophenones would favor the reaction. However, higher yields are obtained

with electron-donating groups for the S3^nthesis of cycUc nitrones, as shown in

equation 6.3.2b

O

O N

E-2

yield(%)

NO- H Me OMe

12.1 33.0 59.1 75.1 (6.3)

Although several cycUc nitrones have been synthesized via this

cycloaddition reaction, neither the detaUed reaction mechanism involving the

nitrosoketene intermediate nor the conformations of nitrosoketene have been

reported. Hence, we undertook the detaUed conformational studies of

nitrosoketene in a gas phase. The cycloaddition mechanisms of nitrosoketene

117

with various nucleophiles were studied using ab initio molecular orbital

theory to understand the experimental observations and to predict the

chemical selectivity of the important reactions involving nitrosoketene.

118

6.1 References

1. TidweU, T. T. Ketenes; John Wiley & Sons: New York, 1995.

2. (a) Katagiri, N.; Kurimoto, A.; Yamada, A.; Sato, H.; Katsuhara, T.; Takagi, K.; Kaneko, C. J. Chem. Soc, Chem. Commun. 1994, 281. (b) Katagiri, N.; Sato, H.; Kurimoto, A.; Okada, M.; Yamada, A.; Kaneko, C. J. Org. Chem. 1994, 59, 8101.

3. (a) Katagiri, N.; Okada, M.; Morishita, Y.; Kaneko, C. J. Chem. Soc, Chem. Commun. 1996, 2137. (b) Katagiri, N.; Okada, M.; Kaneko, C. Tetrahedron Lett. 1996, 37, 1801.

4. Ham, S.; Birney, D. M. Tetrahedron Lett. 1994, 35, 8113.

119

CHAPTER \TI

RESULTS AND DISCUSSION

7.1 Conformations of Nitrosoketene

McAUister and TidweU have calculated an energy of an unspecified

conformation of nitrosoketene and reported a carbonyl stretching frequencies

computed at the RHF/6-31G* i and MP2(FuU)/6-31G* 2.3 level. For the

investigation of the nitrosoketene identity and the preferred conformation in

a gas phase, we optimized the geometries and calculated the vibrational

spectra for both E- and Z-conformations at the RHF/6-31G* and MP2(FC)/6-

31G* level.

O /O

o-^ '^O

E-1 2-1

These ab initio calculations were performed using Gaussian 92 4 and

Gaussian 94.^ The absolute energies calculated at the MP2(FC)/6-3lG* level

are reported in Table 7.1. The relative energies were computed at the

MP4(SDQ)/6-31G* level with the geometries optimized at the MP2/6-31G*

level using scaled (0.9626) zero-point energy corrections ^ and are Usted in

120

Table 7.2. The infrared absorbances were calculated at the MP2(FC)/6-3lG*

level and the predicted absorbances are scaled using scaling factor of 0.9427

as recommended by Pople et al.,^ while the carbonyl stretches of ketenes are

scaled using the factor of 0.960 as recommended by Kappe et al.,'^ and are

shown in Table 7.3.

Table 7.1. Absolute Energies of Z- and E-Nitrosoketene in Hartrees. Optimized at the MP2/6-31G* level

RHF/6-31G*a ZPEb MP2/6-31G* MP4(SDQ)/6-31G*

Z-1 -280.361967 19.0 -281.124579 -281.137007

E-1 -280.364691 18.9 -281.125998 -281.138668

a Optimized at the RHF/6-31G* level, b Calculated at the RHF/6-31G* level.

Table 7.2. Relative Energies, Entropies, Dipole Moments of Z- and E-Nitrosoketene in kcal/mol, Optimized at the MP2/6-31G* Level

RHFa.b MP2a MP4(SDQ)+ZPE«.'= S^ ju(Dy

Z-1 0.9 1.0 1.1 70.5 3.451

E-1 0.0 0.0 0.0 70.1 2.877

a Relative energy in kcal/mol. b Optimized at the RHF/6-31G* level. ^ Scaled by 0.9646. ^ Entropy in cal/mol«K, unsealed. ^ Dipole moment in cm-i

121

Table 7.3. Vibrational Frequencies Calculated for Both Z- and E-Nitrosoketene at the MP2/6-31G* Level

band

C=0

N = 0

C=C

C=0

N = 0

C=C

freq (cm-i)

MP2/6-31G*

2206

1487

1346

2223

1469

1369

scaled freq (cm-i)

(0.9427)

Z-1

2080

1402

1269

E-1

2096

1385

1291

(0.960)

2118

2134

intensity

(km/mol)

536

22

296

655

85

60

EnergeticaUy, E-1 is calculated more stable than Z-1 by only 1.1

kcal/mol at the MP4(SDQ)/6-3lG* + ZPE level (Table 7.2). It has previously

been suggested that a balance between electrostatic and steric effects

determine the conformational preferences of substituted a-oxoketenes.8 The

energy preference found for E-1 would imply that the electrostatic attraction

between the non-bonding electrons on the nitrogen (which nonetheless bears

a net positive charge) and the partially positive central carbon (C2) in the

122

ketene is stronger than the electrostatic attraction between this carbon and

the partially negative nitrosyl oxygen (05) in Z-1.

The infrared (IR) spectrum of the product mixture from the thermal

decomposition of isonitroso Meldrum's acid provided experimental evidence

for the IR spectra of the nitrosoketene.^ Peaks at 1314 cm-i and 2146 cm-i

were then assigned as the C=C stretching and C=0 stretching modes of

nitrosoketene, respectively. In Table 7.3, the differences of calculated

frequencies for C=0 and C=C stretches between E-1 and Z-1 are 16 ~ 22 cm-i.

which is within the mean absolute error of the MP2 carbonyl frequency for

acetylketene. 8 Therefore, an accurate assignment of nitrosoketene

conformation generated from isonitroso Meldrum's acid decomposition cannot

be made by the comparison of vibrational frequencies between experimental

data and ab initio calculations.

The intensities, however, are computed quite different for the E- and

Z- conformers as shown in Table 7.3. The overall calculated intensity pattern

is compared with the experimental peak intensity in Figure 7.1. The

calculated pattern for the Z-1 correlates better with the experimental

intensity pattern. However, this comparison is not sufficient to conclude that

the gas phase conformation of nitrosoketene is Z.

123

>

Q:

Computed Z-nitrosoketene IR spectrum

I

Computed E-nitrosoketene IR spectrum

I I

Experimental nitrosoketene FTIR spectrum

I I 1400 1600 1800

Energy (cm"'')

2000

Figure 7.1. Comparison of the computed IR spectra for Z-1 and E-1 with the experimental FTIR spectrum. Relative intensities are normalized to the C=0 stretch band.

124

The conformation of nitrosoketene from isonitroso Meldrum's acid is

not conclusively determined at this point from the comparison between

experimental Fourier transform infrared spectroscopy (FTIR) and the ab

initio calculated IR spectra. However, the frequencies are in agreement in the

comparison for both conformers, supporting the suggestion that nitrosoketene

is the observed product from isonitroso Meldrum's acid decomposition.

7.2 Cycloaddition of Nitrosoketene

The asynchronicity that we had calculated for the addition of

nitrosoketene with formaldehyde at the RHF/6-31G* level suggested that

electron deficient ketones would react faster than electron rich ones.i^

However, the experimental results with substituted acetophenones showed

the opposite trend, n Clearly, either earUer RHF calculations were misleading

or formaldehyde is not a good model for ace top he none. Thus, we reexamined

the cycloaddition of 1 with formaldehyde at the higher level of MP2/6-31G*

and investigated the cycloadditions of 1 with acetone and propenal (eq 7.1).

125

o o

o

o E-1 2

a R.|—H, R2—H

b R.|=CH3, R2=CH3

c R.)=H, R2=CHCH2 (~ i \

The ab initio molecular orbital calculations were carried out using

Gaussian 94.^ Geometries were optimized at the RHF/6-31G* level and

characterized by vibrational frequency calculations. The structures were then

reoptimized at the MP2(FC)/6-3lG* level; these are shown in Figure 7.3 and

7.5 and 7.6. Relative energies were calculated at the MP4(SDQ)/6-31G* level

using the MP2/6-31G* optimized geometries and are reported in Table 7.4.

Zero-point energy (ZPE) corrections were obtained from RHF/6-31G*

frequencies and scaled by 0.9135, as recommended by Pople et al.^

126

Table 7.4. Relative Energies (kcal/mol) of Structures Optimized at the MP2/6-3IG* Level

Structure

E-1 + CH2O

2aTS [3+2]

2a

3aTS [4+2]

3a

RHF a

Addition

0.0

13.3

-41.1

18.6

-49.7

MP2 MP4(SDQ)

of formaldehyde to 1

0.0

-1.0

-53.9

3.8

-51.3

0.0

3.8

-47.7

9.7

-50.9

MP4(SDQ)+ZPE b

0.0

4.8

-42.8

10.3

-45.8

Addition of acetone to 1

iJ-1 + acetone

2bTS [3+2]

2b

3bTS [4+2]

3b

0.0

14.2

-36.2

16.8

-41.8

0.0

-2.5

-55.4

2.8

-48.7

0.0

2.6

-47.5

7.3

-47.3

0.0

4.5

-41.6

9.0

-41.7

Addition of propenal to 1

E-1 + propenal

2cTS [3+2]

2c

3cTS [4+2]

3c

0.0

15.3

-31.1

17.9

-40.7

0.0

0.0

-47.4

4.6

-45.0

0.0

5.2

-40.9

9.5

-44.8

0.0

7.3

-35.3

11.2

-39.2

^ Optimized at the RHF/6-31G* level, b Zero-point vibrational energy correction from RHF/6-31G* frequencies and scaled by 0.9135, reference 6.

127

For all three systems we have studied (formaldehyde, acetone, and

propenal) the [3+2] pathway is favored over the [4+2] which is consistent

with our earUer RHF calculations. Furthermore, the dioxazinones (3) are

generaUy calculated to be more stable than the nitrones (2). This suggests

that the proposed rearrangement from 3 to 2 is unlikely involved in the

formation of the sole observed product 2. The barriers for pseudopericycUc

reactions can be ver}- low as shown in Table 7.4. The low barrier is

contributed by the lack of cycUc overlap in pseudopericycUc orbital

interactions!- in planar transition states as shown in Figure 7.2.

Orbital Orthogonalities

O O [3+2]

E-1

O O

O

Figure 7.2. PseudopericycUc orbital interactions in 2TS

128

The in-plane 7i-system of the ketone oxygen (08, see Figure 7.3) adds

as a nucleophile at C2 to the in-plane 7r*-orbital of the ketene to make the

C208 bond. In turn, the in-plane lone pair of the nitrogen (N5) adds as a

nucleophile at C7 to the n* of the ketone. Those two orbital interactions are

orthogonal to the out-of-plane conjugated Ti-system of nitrosoketene.

7.2.1 Formaldehyde addition

The MP2/6-31G* calculation, which accounts for some electron

correlation effects, i on the formaldehyde addition to nitrosoketene shows

that the nucleophilic attack from the ketene nitrogen (N5) leads in the planar

[3+2] reaction pathway (2aTS), as previously calculated at the RHF level, i

However, the [4+2] transition state (TS) is qualitatively different at the two

levels of theory. At the RHF/6-31G* level, the TS is close to planar, and C208

bonding is more advanced. At the MP2/6-31G* level, the formaldehyde is

above the plane of the ketene (3aTS), and asynchronous N5 nucleophilic

attack leads the reaction (Figure 7.3). The [3+2] pathway is still calculated to

be favored over the [4+2]. However, N5C7 bonding in 2aTS still leads; the

higher level of theory used here CMP2/6-31G*) does not resolve the

discrepancy between Katagiri's experimental results and the calculations.

129

(0.153)

1.402

2a

3aTS (0.173) 3a

Figure 7.3. Geometries for [3+2] and [4+2] cycloaddition of nitrosoketene with formaldehyde, optimized at the MP2/6-

o

31G* level. Bond lengths are in Anstroms. Two views are shown. Partial bonds are unfilled. Asynchronicity is in parenthesis.

130

7.2.2 Acetone Addition

We examined the cycloaddition of nitrosoketene with acetone, the

simplest ketone, which we expected would be less susceptible to nucleophilic

attack than formaldehyde, for three reasons. First, steric hindrance by two

methyl groups should reduce the extent of N5C7 or 06C7 bonding in both

2bTS and 3bTS (Figure 7.4). Secondly, stabiUzation of carbonyl carbon (C7)

makes it less susceptible to nucleophiUc attack from N 5 or 06 of

nitrosoketene. Thirdly, considering two possible resonance structures in the

TS (Figure 7.5), the resonance structure A is favored with R=Me over B.

131

i : 1.394

3bTS (-0.055)

Figure 7.4. Geometries for [3+2] and [4+2] cycloaddition of nitrosoketene with acetone, optimized at the MP2/6-31G*

o

level. Bond lengths are in Anstroms. Two views are shown. Partial bonds are unfiUed. Asynchronicity is in parenthesis.

132

o 6+ s

N (-.^2

O ^ ^1 B

Figure 7.5. Resonance structures in 2TS

Indeed, C208 bond formation is increased and N5C7 and 06C7 bond

formation are decreased in both 2bTS and 3bTS, relative to the

formaldehyde reactions. The asynchronicity is yet not in accord with the

experimental results. Despite the increased steric hindrance, the barriers for

the cycloadditions with acetone are lower than for formaldehyde. This

presumably reflects the additional stabilization of resonance structure A in

Figure 7.5. The [3+2] pathway remains favored.

133

7.2.3 Propenal Addition

Finally, propenal, the simplest conjugated carbonyl compound, was

used as a model for acetophenone. In both 2cTS and 3cTS, the nucleophiUc

attack of the ketone oxygen (08) leads the reaction and the electrophiUc

addition of the ketene (X5 or 06) to the carbonyl carbon (C7j foUows (Figure

7.6). This is consistent with the experimental data in which acetophenones

having an electron-donating group faciUtate the cycloaddition reaction with

nitrosoketene (eq 6.3). In 2cTS, the resonance structure A (in Figure 7.5) is

stabiUzed by conjugation from the adjacent vinyl group, whereas resonance

structure B is destabiUzed by loss of conjugation. The net result as compared

to both acetone and formaldehyde is a higher barrier and more advanced

C208 bonding, with the [3+2] pathway stiU favored.

134

1.398

(-0.071)

3cTS (-0.159) 3c

Figure 7.6. Geometries for [3+2] and [4+2] cycloaddition of nitrosoketene with propenal, optimized at the MP2/6-31G* level. Bond lengths are in Anstroms. Two views are shown. Partial bonds are unfilled. Asynchronicity is in parenthesis.

135

An experimental comparison between conjugated and unconjugated

ketones is avaUable; Katagiri et al. has reported that the yield of 2d is higher

than 2e (eq 7.2).ii This result appears in conflict with the calculated higher

barrier for 2cTS as compared to 2bTS. We note, however, that 5 is very

electron rich, which would be expected to lower the barrier as compared to

propenal.

O

^ ^ E.2 A O .AJ^. Me ^ ^ OMe [3^2] / ' I ^ ^ ^ O M e

O ^ Me

2e

(7.2)

7.3 Conclusions

Transition states for the cycloadditions of nitrosoketene with

formaldehyde, acetone and propenal were computed at the MP2/6-31G* level.

The [3+2] cycloadditions of nitrosoketene (1) with ketones are

computationally preferred to the alternative [4+2] pathway with a

136

significantly lower barrier. The greater stability of the [4+2] products makes

1,2-rearrangement unlikely to occur. The sense of asynchronicity with

propenal in the [3+2] cycloaddition is reversed from ones with formaldehyde

and acetone. Apparently, the nucleophilic attack of the nitrosoketene

nitrogen on the carbonyl carbon of propenal is disfavored because it disrupts

the conjugation. This indicates that the leading interaction is nucleophilic

attack of the carbonyl oxygen on the ketene carbon as shown in the

calculated asynchronicity. This is consistent with the observed substituent

effects measured experimentally.

137

7.4 References

1. Gong, L.; McAllister, M. A.; TidweU, T. T. J. Am. Chem. Soc. 1991, 113, 6021.

2. McAllister, M. A.; TidweU, T. T. Can. J. Chem. 1994, 72, 882.

3. McAllister, M. A.; TidweU, T. T. J. Org. Chem. 1994, 59, 4506.

4. Frisch, M. J.; Trucks, G. W.; Head-Gordon, M.; GiU, P. M. W.; Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M. A.; Replogle, E. S.; Comports, R.; Andres, J. L.; Raghavachari, K.; Binkley, J. S.; Gonzalez, C; Martin, R. L.; Fox, D. J.; Defrees, D. J.; Baker, J.; Stewart, J. J. P.; Pople, J. A. Gaussian 92. Gaussian, Inc.: Pittsburgh PA, 1992.

5. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; GiU, P. M. W.; Johnson, B. G.; Robb, M. A.; Chessemen, J. R.; Keith, T.; Petersson, G. A.; Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. J. P.; Head-Gordon, M.; Gonzalez, C; Pople, J. A. Gaussian 94, Revision D.3; Gaussian, Inc.: Pittsburgh PA, 1995.

6. Pople, J. A.; Scott, A. P.; Wong, M. W.; Radom, L. Isr. J. Chem. 1993, 345.

7. Kappe, C. O.; Wong, M. W.; Wentrup, C. J. Org. Chem. 1995, 60, 1686.

8. Birney, D. M. J. Org. Chem. 1994, 59, 2557.

9. (c) Matsui, H.; Zuckerman, E. J.; Katagiri, N.; Kaneko, C; Ham, S.; Birney, D. M. J. Phys. Chem. A 1997, 101, 3936.

10. Ham, S.; Birney, D. M. Tetrahedron Lett. 1994, 35, 8113.

11. Katagiri, N.; Sato, H.; Kurimoto, A.; Okada, M.; Yamada, A.; Kaneko, C. J. Org. Chem. 1994, 59, 8101.

138

12. (a) Birney. D. M.: WagenseUer. P. E. J. Am. Chem. Soc 1994, 116, 6262. (b) WagenseUer. P. E.; Birney. D. M.; Roy, D. J. Org. Chem. 1995. 60. 2853. (c) Ham, S.; Birney, D. M. J. Org. Chem. 1996. 61, 3962. (d) Birney. D. M.: Ham. S.: Unruh, G. R. J. Am. Chem. Soc. 1997. 119. 4509.

13. Hehre, W. J.: Radom. L.: Schleyer. P. v. R.: Pople, J. A. Ab Initio Molecular Orbital Theory: John WUey and Sons, Inc.: New York. 1986.

139

PART THREE

THERMAL CHELETROPIC DECARBONYLATIONS

140

CHAPTER \TII

BACKGROUND

Cheletropic reactions as defined by Woodward and Hof&nann are those

processes in which two a bonds which terminate at a single atom are made,

or broken, in concert, i Among all the classes of pericyclic reactions, the

cheletropic fragmentation has been of particular interest because they are

the only class for which two orbital symmetry aUowed pathways were

proposed. The departing motions are described as Unear or non-Unear on the

single atom fragment, and conrotatory or disrotatory on the other

fragment.! 2

The decarbonylations of 3-cyclopentenone and its derivatives have

been extensively studied, - including measurements of the rotational and

vibrational energy distributions in the extruded carbon monoxide." Based on

the orbital symmetry rules by Woodward and Hof&nann, i the

decarbonylation of 3-cyclopentenone was expected to follow either a Unear

disrotatory or a non-Unear conrotatory pathway. The ground state of 3-

cyclopentenone (1) and the transition state for the cheletropic

decarbonylation have been calculated at several different levels of theory

(Figure 8.1).5.8

141

O

o. \ \

'^

1

^2v

ITS

C.

y^

2

O2

CO

Relative Energy- (MP4(FC.SDTQ)/D95**//MP2/6-31G* + ZPE)^ 0.0 kcal/mol 49.0 kcal/mol 18.9 kcal/mol

Figure 8.1. Cheletropic decarbonylation of 3-cyclopentenone (1). The symmetrj^ of the compounds and the relative energies are shown, calculated at the MP4(FC,SDTQ)/D95** level from the MP2/6-31G* optimized geometries, with zero-point energy- correction.

Two aUowed pathways were predicted by Woodward and Hoffmann for

the decarbom'lation of 1. One is the Hnear-suprafacial whUe disrotatory on

butadiene and the departure of CO is not along the molecular axis. The other

is the nonlinear-antarafacial (conrotatory). 1 The calculated transition

state^3- '8 ^-as i^ consistent with the former. Furthermore the evidences based

on the shock-tube experiments by Simpson et al.'^ also supported the Unear

disrotatory- pathway as presented in Figure 8.2.

142

CO LUMO

CO HOMO

Butadiene LUMO

ITS

Figure 8.2. Orbital interactions in the decarbonylation of ITS

The decarbonylation of bicyclo[2.2.1]hepta-2,5-dien-7-one (3) was of

interest8-io in comparison to that of 1 and was also calculated at the MP4(FC,

SDTQ)/D95** single point energy level from the MP2/6-31G* optimized

geometries (Scheme 8.3).8

143

3 4

-H CO

Relative Energy (MP4(FC.SDTQ)/D95**//MP2/6-3lG* + ZPE)8 0.0 kcal/mol 15.2 kcal/mol -32.5 kcal/mol

Figure 8.3. Cheletropic decarbonylation of bicyclo[2.2.1]hepta-2,5-dien-7-one (3). The symmetry of the compounds and the relative energies are shown, calculated at the MP4(FC,SDTQ)/D95** level from the MP2/6-31G* optimized geometries.

This reaction is substantially exothermic and as a result, has a much

lower barrier than the previous one, although the CO departure pathway was

similar to that of 1 following the hnear-suprafacial pathway.8

We have calculated a number of [4+2] and [3+2] cycloaddition

reactions as weU as 1,3- and 1,5- hydrogen shifts involving several conjugated

ketenes as discussed in this dissertation.8.ii Those mechanisms were

explained by pseudopericyclic orbital topologies. A distinctive feature of

144

pseudopericyclic transition states is their tendency to adopt planar

geometries. However, steric crowding in [4+2] reactions of oxoketenes and

imidoylketenes leads to slight distortions from planarity in the transition

states.iib.c Recent appUcations of decarbonylations include the formation of a-

oxoketenes and imidoylketenes from their precursors, furan-2,3-dionesi213

and pyrrole-2,3-diones,i4 respectively. We recognized that the

decarbonylations of furan-2,3-diones and pyrrole-2,3-diones could potentially

proceed via such a planar, pseudopericyclic pathway. Furthermore, these

[4+1] cheletropic decarbonylations should be stericaUy less crowded, which

would reflect pure electronic effects rather than steric ones to the transition

geometries.

Another distinguishing character of pseudopericyclic reactions is the

orbital disconnections around the interacting loop of orbitals. All of the

pseudopericyclic transition states introduced up to this point in this

dissertation contain two orbital disconnections. However, the question still

remains to be answered; how many and what type of orbital disconnections

are necessary to allow the benefits of pseudopericyclic reaction pathway?!^ In

Lemal's original description in the pseudopericyclic reaction, there was a

single disconnection in the degenerate sulfoxide rearrangement of

perfluoromethyl (Dewar thiophene S-oxide, 5) (Figure 8.4).2

145

F.C

Orbital Disconnection

Figure 8.4. Single orbital disconnection in the facile degenerate rearrangement of perfluoromethyl (Dewar thiophene S-oxide, 5)

A single orbital disconnection was also shown in Woodward and

Hoffmann's nonUnear pathway for the decarbonylation of cyclopropanone. i

However, there are, in fact, three possible orbital interactions which should

be considered, as shown in Figure 8.5.8

146

Orbital Disconnection

G^O"

B 4 e', No Orbital Disconnection

2 e", No Orbital Disconnection

OC3

Figure 8.5. Possible orbital interactions in the nonlinear decarbonylation of cyclopropanone. (A) The departing CO with one orbital disconnection. (B) The departing CO is sp2 hybridized. This is anti-aromatic four electron systems. (C) The primary interaction is between TT* of CO and the n of e the no. This is two electron, aromatic system.

We therefore carried out ab initio calculations on the thermal

decarbonylations of 3-cyclopentenone derivatives. This study explores the

effects of the number and the type of orbital disconnections on these

reactions. In this sense, the broader implications for the general

understanding of pseudopericyclic reactions are examined.

147

8.1 References

1. Woodward, R. B.; Hoffmann, R. Angew. Chem. Int. Ed. Engl. 1969, 8, 781.

2. Lemal, D. M.; MaGregor, S. D. J. Am. Chem. Soc 1996, 88, 1335.

3. Bevan, J. W.; Logon, A. C. J. Chem. Soc, Faraday Trans. 2 1973, 69, 902-925.

4. (a) Lewis, J. D.; Laane, J. Spectrochim. Acta 1975, 31A, 755-763. (b) Gordon, R. D.; Orr, D. R. J. Mol. Spectrose 1988, 129, 24-44.

5. (a) Bencivenni. L.; Ramondo, F.; Quirante, J. J. J. Mol. Struct. (Theochem) 1995, 330, 389-393. (b) Quirante, J. J.; Enriquez, F. Theor. Chim. Acta, 1994, 89, 251-259. (c) Rzepa, H. S. J. Chem. Res. (S) 1988, 224-225.

6. Unruh, G. R. Ph. D. Thesis, Texas Tech University, 1995.

7. (a) Simpson, C. J. S. M.: Price, J.; Holmes, G.: Adam, W.: Martin, H.-D.; Bish, S. J. Am. Chem. Soc. 1990, 112, 5089-5094. (b) Jimenez, R.; Kable, S. H.; Loison, J . -C: Simpson, C. J. S. M.; Adam, W.; Houston, P. L. J. Phys. Chem. 1992, 96, 4188-4195. (c) Prather, K. A.; Rosenfeld, R. N. J. Phys. Chem. 1991, 95, 6544-6548.

8. Birney, D. M.; Ham, S.; Unruh, G. R. J. Am. Chem. Soc 1997. 119, 4509-4517.

9. Birney, D. M.; Berson, J. A. Tetrahedron 1986, 34, 1561-1570.

10. (a) LeBlanc, B. F.; Sheridan, R. S. J. Am. Chem. Soc 1985, 107, 4554-4555. (b) Birney, D. M.; Berson, J. A. J. Am. Chem. Soc 1985, 107, 4553-4554.

148

11. (a) Ham, S.: Birney, D. M. Tetrahedron Lett. 1994, 35, 8113-8116. (b) Wagenseller, P. E.; Birney. D. M.: Roy, D. J. Org. Chem. 1995, 60, 2853-2859. (c) Ham, S.: Birney, D. M. J. Org. Chem. 1996, 61, 3962-3968. (d) Birney, D. M. J. Org. Chem. 1996. ^i ,243. (e) Matsui, H.: Zuckerman, E. J.; Katagiri, N.; Sugihara, T.; Kaneko, C ; Ham, S.; Birney, D. M. J. Phys. Chem. A 1997, 101, 3936-3941. (f) Ham, S.; Birney, D. M. Tetrahedron Lett. 1997, 38, 5925-5928. (g) Birney, D. M.; Xu, X.: Ham, S. J. Org. Chem. 1997, 62, 7114-7120.

12. (a) Kappe, C. O.; KoUenz, G.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 485-486. (b) Chuburu, F.; Lacombe, S.; GuUouzo, G. P.: Wentrup, C. New. J. Chem. 1994, 18, 879-888.

13. Wentrup, C ; HeUmayer, W.; Kollenz, G. Synthesis 1994, 1219-1248.

14. (a) Kappe, C. O.; KoUenz, G.; Netsch, K.-P.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 488-490. (b) Kappe, C. O.; KoUenz, G.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 487-488. (c) FuUoon, B.; El-Nabi, H. A. A.; KoUenz, G.; Wentrup, C. Tetrahedron Lett. 1995, 36, 6547-6550. (d) MasUvets, A. N.; Krasnykh, O. P.; Smirnova, L. I.; Andreichikov, Y. S. J. Org. Chem. (USSR) 1989, 941-948.

15. This question was recently raised in the electrocycUzations of vinylaUenes.16

16. Lopez, S.; Rodriguez, J.; Roy, J. G.; Lera, A. R. D. J. Am. Chem. Soc.

1996, 118, 1881-1891.

149

CHAPTER IX

RESULTS AND DISCUSSION

9.1 Introduction

The decarbonylations of furandiones have been used for a generation of

a-oxoketene under the photochemical and thermal conditions.! The thermal

conditions are carried out by flash vacuum pyrolysis (FVP) above

approximately 200 to 300 ^C. The only byproduct, carbon monoxide has a

single IR absorption which does not interfere with other product peaks,

allowing for ready identification of the ketene products by matrix isolation IR

spectroscopy. Thermal decarbonylations of pyrrole dione s2 have been also

used to generate a variety of imidoylketenes as a intermediates and for the

identification by IR spectroscopy. However, the activation energies for those

decarbonylations have not been determined.

We have carried out ab initio calculations of these thermal

decarbonylations of furandione and pyrroledione to elucidate the detailed

mechanisms and the energetics in the light of the pseudopericylic orbital

topology. Furthermore, the comparison between those pseudopericyclic

decarbonylations and pericyclic decarbonylations provides more general

understanding and synthetic applications of important organic reactions.

150

9.2 Computational Methods

The ab initio molecular orbital calculations were carried out using

Gaussian 92^ and Gaussian 94.4 Geometry optimizations were performed first

at the RHF/6-31G* level and then at the MP2(FC)/6-31G* level. Frequency

calculations verified the identity of each stationary point as a minimum or

transition state. Single point energies of each structure were obtained at the

MP4(FC,SDTQ)/D95** level. The double-: basis set, D95**. has polarization

functions on aU atoms.^ The zero-point energ>- (ZPE) corrections were

obtained by scaling the MP2/6-31G* ZPE by 0.9646. as recommended by

Pople et al.^ Unless otherwise indicated, all energies discussed in here are

MP4(FC.SDTQ)/F95** with scaled ZPE correction. Absolute energies are in

the Appendix and the relative energies are reported in Tables 9.1 and 9.2.

The decarbonylation reactions with two orbital disconnections are shown in

Scheme 9.1.

•O

•O

H

H "O

O

+ CO

H

H ^ N

4

O

+ CO

Scheme 9.1

151

9.3 Thermal Decarbonylation of Furandione

The optimized transition state (ITS) for the decarbonylation of 1 is

shown in Figure 9.1. The distinguishing feature of ITS compared to the

pericyclic transition states of 3-cyclopentenone and 2,3-norborradien-7-one

(see Chapter VIII) is its planarity which is a consequence of the

pseudopericyclic orbital topology.

1.552 AR=0.395

AR=0.704

153.3'

1 ITS

Asynchronicity = 0.309

Figure 9.1. Geometries for the decarbonylation of furandione, optimized at the MP2/6-31G* level. Two views are shown. Partial bonds are unfilled. Bond distances are in angstroms.

152

When viewed as an addition of CO to a ketene, two sets of orbital

interactions are involved: the in-plane orbital system reflects a nucleophilic

addition of the CO lone pair to the ketene carbon, the out-of-plane orbital

system reflects the LUMO of the CO acting as an electrophile towards the

lone pair from the carbonyl oxygen (Figure 9.2). The transition state 1 is

optimized as concerted, asynchronous. From 1 to ITS, the C2-03 bond is

elongated by 0.704 A, while the C2-C3 bond is only lengthened by 0.396 A. It

is clear from the transition state geometry that electron donation from the

lone pair of CO dominates the reaction of forming 1. The C6-C2-01 angle is

close to linear (153.3 °). This is also consistent that nucleophilic addition of

carbon monoxide to the ketene carbon leads the reaction.

out-of-plane in-plane

lone pair

Figure 9.2. Out-of-plane and in-plane orbitals in the cheletropic decarbonylation of furandione (1)

153

The calculated activation barrier for the decarbonylation of 1 is 19.2

kcal/mol (Table 9.1). The reaction is computed to be 4.5 kcal/mol

endothermic. When the energetics are compared to the decarbonylation of the

3-cyclopentenone (Figure 8.1), the foUowing were observed. The barrier for

the 3-cyclopentenone is 49.0 kcal/mol with an endothermicity of 18.9 kcal/mol

at the same level of theory.' Thus, the decarbonylation of 3-cyclopentenone is

14.5 kcal/mol more endothermic, yet 29.8 kcal/mol higher barrierl Based on

the Hammond postulate8 or the BeU-Evans-Polanyi principle,^ for similar

reactions, more exothermic reactions should have lower activation energies.

The much lower barrier for the decarbonylation of 1 is attributed by the

planar, pseudopericycUc orbital overlap which avoids electron-electron

repulsion in the transition state.i^ On the other hand, the decarbonylation of

3-cyclopentenone with no orbital disconnection requires pericyclic orbital

interaction in the transition state, resulting in a high activation barrier.

154

Table 9.1 Relative Energies (in kcal/mol) for the Decarbonylation of Furandione, Optimized at the MP2/6-31G* Level

Level of Theory

RHF/6-31G*^

MP2/6-31G*b

RHF/D95**

MP2/D95**b

MP3/D95**b

MP4(SDQ)/D95**b

MP4(SDTQ)/D95**b

MP4(SDTQ)+ZPEc

1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

ITS

33.3

25.0

34.9

25.4

35.2

27.9

21.9

19.2

2

0.5

10.5

4.0

11.6

14.8

9.1

8.9

4.5

a RHF/6-31G* geometry optimization, b Frozen core approximation. ^ Scaled by 0.9646, reference 6.

155

9.4 Thermal Decarbonylation of Pyrroledione (3)

The two systems, furandione (1) and pyrroledione (3) are isoelectronic.

thus we anticipated the transition state 3TS would be planar. Howe\-er. the

transition structure 3TS was calculated to be sUghtly out-of-plane. The

planar second order saddle point structure (3TS') is 0.3 kcal/mol higher than

the transition state. The large imaginary- frequency (362.9i cm-i) corresponds

to decarbonylation. However, there is a smaU imaginary frequency (93.2z

cm-i) corresponding to an out-of-plane motion of the nitrogen. The

geometrical aspects of 3TS are simUar to those of ITS. It is a concerted and

asynchronous transition state, with C2C6 bond more lengthened than C2X3

bond towards forming the ketene and CO. The angle for 01-C2-C6 is 150.9

°C. Again, in considering the reaction between imidoylketene 4 and carbon

monoxide, nucleophiUc attack of carbon monoxide to the ketene carbon leads

the formation of pyrroledione (Figure 9.3).

156

AR=0.425

150.9°

AR=0.746

3 3TS

Asynchronicity = 0.321

150.6°

3TS'

Figure 9.3. Geometries for the decarbonylation of pyrroledione, optimized at the MP2/6-31G* level. Two views are shown. Partial bonds are unfilled. Bond distances are in angstroms.

157

The calculated activation barrier for the decarbonylation of 3 is 34.5

kcal/mol which is substantially higher than that (19.2 kcal/mol) of 1 (Table

9.2). This may be because the reaction of 3 is more endothermic (19.0

kcal/mol) than that of 1 (4.5 kcal/mol). The resonance of amide is stronger

that ester which contributes to the higher activation barrier for the

decarbonylation of 3. Also, making C=0 double bond in 2 is

thermodynamically more favorable than making a C=N double bond in 4.

Table 9.2. Relative Energies (in kcal/mol) for the Decarbonylation of Pyrroledione, Optimized at the MP2/6-31G* Level

Level of Theory

RHF/6-31G*^

MP2/6-31G*b

RHF/D95**

MP2/D95**b

MP3/D95**b

MP4(SDQ)/D95**b

MP4(SDTQ)/D95**b

MP4(SDTQ)+ZPEc

3

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

3TS

48.4

40.9

50.4

41.4

48.5

42.9

37.5

34.5

3TS'

d

40.7

51.1

41.3

48.5

43.2

37.6

34.8

4

15.3

25.7

20.3

27.2

28.0

23.3

23.4

19.0

a RHF/6-31G* geometry optimization, b Frozen core approximation. ^ Scaled by 0.9646, reference 6. ^ The transition state was planar at the RHF/6-31G* level.

158

Experimentally, pyrrolediones are reported to extrude carbon

monoxide at temperature range from 160 to 185 ^C in static systems or above

300 °C under FVP conditions.2 This compares to furandione which

decarbonylates at temperatures of 110 ^C at static systems or 200-250 °C

under FVP conditions.! Although qualitative, the calculated energetics are in

agreement with the observed experiments.

9.5 Decarbonylations with One Orbital Disconnection

The decarbonylations of furandione and pyrroledione contain two

orbital disconnections in the interacting loop of orbitals, which allows

pseudopericyclic orbital topology. Now, the systems with only one orbital

disconnection in the orbital overlap are introduced below (Scheme 9.1)."

N _ -co^ [>=o o -CO

o 8

y^

^ . o

o

o

10

CO ^

11

O rio o

12

CO

o

13

Scheme 9.1

159

Birney et al. discussed those systematic series of decarbonylations.'

Based on the geometries of those transition structures and the

thermodynamics of each reactions, it was concluded that one orbital

disconnection may lead to a (nearly) planar pseudopericyclic transition state.^

However, in an asynchronous transition state, if the disconnection is at the

site of strongest bond formation, the reaction wiU have more pseudopericycUc

character.

9.6 Conclusions

Transition structures for the decarbonylations of furandione and

pyrroledione were located at the MP2/6-31G* level. Relative energies of these

and of reactants and the products were calculated at the MP4(FC,

SDTQ)/D95** + ZPE level. Transition structures ITS and 3TS are optimized

to be planar and nearly so, as a consequence of the pseudopericyclic orbital

topology. The shorter C2-C6 bond extensions found in both transition states

indicates tha t the nucleophilic attack from the lone pair of carbon monoxide

to the ketene carbon leads the ring formation of 1 and 3.

Two orbital disconnections at the reaction sites with favorable

interactions between nucleophile and electrophile result substantially low

activation barriers. These barriers are much lower than those found in the

decarbonylations of 3-cyclopentenone and of bicyclo[2.2.1]hepta-2,5-dien-7-

160

one, which contain no orbital disconnections, and consequently require

conventional pericyclic orbital overlap.

A single orbital disconnection at the site of strongest bond formation

may be sufficient to impart pseudopericyclic character to the transition state.

This may result in somewhat lower barriers and nearly planar transition

states.

161

9.7 References

1. (a) Wentrup, C; Heilmayer, W.; Kollenz, G. Synthesis 1994, 1219-1248. (b) Kappe, C. O.; Wong, M. W.; Wentrup, C. J. Org. Chem. 1995, 60, 1686-1605.

2. (a) Fulloon, B.; El-Nabi, H. A. A.; Kollenz, G.; Wentrup, C. Tetrahedron Lett. 1995, 36, 6547-6550. (b) Fulloon, B.; Wentrup, C. J. Org. Chem. 1996, 61, 1363-1368. (c) Kappe, C. O.; Kollenz, G.; Leung-Toung, R.; Wentrup, C. J. Chem. Soc, Chem. Commun. 1992, 487-490.(d) Maslivets, A. N.; Krasnykh, O. P.; Smirnova, L. I.; Andreichikov, Y. S. J. Org. Chem. (USSR) 1989, 941-948.

3. Frisch, M. J.; Trucks, G. W.; Head-Gordon, M.; GiU, P. M. W.; Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M. A.; Replogle, E. S.; Gomperts, R.; Andres, J. L.; Raghavachari, K.; Binkley, J. S.; Gonzalez, C; Martin, R. L.; Fox, D. J.; Defrees, D. J.; Baker, J.; Stewart, J. J. P.; Pople, J. A. Gaussian 92. Gaussian, Inc.: Pittsburgh PA, 1992.

4. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; GiU, P. M. W.; Johnson, B. G.; Robb, M. A.; Chessemen, J. R.; Keith, T.; Petersson, G. A.; Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. J. P.; Head-Gordon, M.; Gonzalez, C; Pople, J. A. Gaussian 94, Revision D.3; Gaussian, Inc.: Pittsburgh PA, 1995.

5. Dunning, T.H.; Hay, P. J. Modern Theoretical Chemistry; Plenum: New

York, 1976.

6. Pople, J. A.; Scott, A. P.; Wong, M. W.; Radom, L. Isr. J. Chem. 1993,

345.

7. Birney, D. M.; Ham, S.; Unruh, G. R. J. Am. Chem. Soc 1997, 119. 4509-

4517.

8. Hammond, G. S. J. J. Am. Chem.Soc. 1955, 77, 334.

162

9. (a) BeU, R. P. Proc R. Soc London, Ser. A 1936, 154, 414. (b) Evans, M. G.; Polanyi, M. Trans. Faraday. Soc 1938, 34, 11-29.

10. Houk, K. N.; Candour, R. W.; Stozier, R. W.; Rondan, N. G.; Paquette, L. A. J. Am. Chem. Soc 1979, 101, 6797-6802.

163

APPENDIX A

iH NMR, 13C NMR, X-RAY AND UV SPECTRA

164

Chemistry- is full of unknowns. A few of them become known here. 1

report iH SMR and i C NMR of new compounds, which I took right before I

sent them (except compounds. 7b and 8b) for elemental analysis. The

compound 7b was very unstable, and readUy decomposed to its starting

material, acetophenone. X-ray data for the compound 8b is reported herein.

165

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' . , ' • '

1 r - r • fc - '

rc3« •

L

' "r ~ \ p " ^ i — .

r ^-' r

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o i cr

o o

X

o

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a

6 o

I

CO

;3

o c

ffi

o o C<i N^^-X

p § ;zi ffi

<N

; - i

s C

t - . < o

TTmrr

o

166

xcrrr

•ccnr

'orr'oc-

"STTTT"

ii

„ ^ T Z - E B '

o CD ru

Tsn^r

rzrzzT-

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• :

o

o

o o

o o m

o o ^

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o

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o r

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CO

o o

o

Sx a

o o

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o o

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ID

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r.. »* o

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o

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c^ ^ ^

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cc o >»

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o

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167

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168

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169

Hdd

170

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TfTTT

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< 3ISE

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cd

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OH O ;-( P

I

CO

ri o PH CO

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p

B.O

in ID

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01

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< 0) ; - i

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fe

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l o

150

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173

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174

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172

0)

a

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ri r Q

1

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P H O ; H

PH CO «^-H

o

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175

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o

< ?!^ZT

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o CD

in CD

o -t-J CO

a;

CD

o o ri

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-( .3

ri ,p

6 ri

cd 1—I

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00

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p

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176

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cm • I-H

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177

w^

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nnjir a^_;:rz2iEr

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181

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183

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184

Table A. 1. Atomic coordinates (x 10^) and equivalent isotropic displacement coefficients (AxlO^)

0(1) 0(2) 0(3) 0(4) N(l) N(2) ' C(l) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(ll) C(12) C(13)

X

6725(2) 8466(2) 5456(1) 7943(1) 7534(2) 7835(2) 7377(2) 6555(2) 6417(2) 7093(2) 7913(2) 8070(2) 6895(2) 5870(2) 6082(2) 7403(2) 8976(2) 8917(2) 10110(3)

* Equivalent isotrop: trace of the orthoi

y

1336(2) 1957(2) 1341(1) 949(1) 1621(2) 1181(2) 1527(2) 755(2) 678(2) 1365(2) 2139(2) 2218(2) 1276(2) 1335(2) 1279(2) 1118(2) 699(2) -598(2) -1107(3)

Lc U defined ;onalized U,.

z

4222(1) 4437(1) -1112(1) -660(1) 4008(1) 554(1) 3190(1) 2749(1) 1980(1) 1660(1) 2125(1) 2897(1) 836(1) 268(1) -450(1) -230(1) 982(1) 1210(1) 1574(2)

as one third tensor

U(eq)

36(1) 45(1) 28(1) 27(1) 27(1) 21(1) 22(1) 25(1) 24(1) 20(1) 23(1) 25(1) 20(1) 24(1) 23(1) 21(1) 24(1) 28(1) 45(1)

of the

i j

Table A.2. Bond lengths (A)

0(1)-N(1) 0(3)-C(9) N(l)-C(l) N(2)-C(10) C(l)-C(2) C(2)-C(3) C(4)-C(5) C(5)-C(6) C(8)-C(9) C(ll)-C(12)

1.229 (3) 1.221 (2) 1.470 (3) 1.378 (3) 1.381 (3) 1.383 (3) 1.398 (3) 1.384 (3) 1.440 (4) 1.527 (3)

0(2)-N(l) 0(4)-C(10) N(2)-C(7) N(2)-C(ll) C(l)-C(6) C(3)-C(4) C(4)-C(7) C(7)-C(8) C(9)-C(10) C(12)-C(13)

1.225 1.210 1.421 1.474 1.390 1.402 1.472 1.357 1.554 1.516

(3) (3) (3) (3) (4) (3) (3) (3) (3) (4)

185

Table A. 3 Bond angles (o)

0 ( 1 ) 0 ( 2 ) C(7) N ( i : c(2: 0 ( 2 ; c(3: c(4: N(2: c(4: 0 ( 3 ; C(8 0 ( 4 N(2

- N ( l ) - 0 ( 2 ) > - N ( l ) - C ( l ) » - N ( 2 ) - C ( l l ) > -C( l ) -C(2 ) l - C ( l ) - C ( 6 ) >-C(3)-C(4) ) - C ( 4 ) - C ( 7 ) ) - C ( 5 ) - C ( 6 ) ) - C ( 7 ) - C ( 4 ) ) - C ( 7 ) - C ( 8 ) ) - C ( 9 ) - C ( 8 ) ) -C(9 ) -C(10 ) ) -C(10 ) -C(9 ) ) - C ( l l ) - C ( 1 2 )

1 2 3 . 9 ( 2 ) 118 .2 (2 ) 125 .3 (2 ) 118 .7 (2 ) 123 .1 (2 ) 120 .8 (2 ) ' 118 .8 (2 ) 120 .5 (2 ) 120 .6 (2 ) 126 .8 (2 ) 133 .0 (2 ) 104 .7 (2 ) 126 ,9 (2 ) 112 .2 (2)

0 ( 1 ) - N ( 1 ) - C ( 1 ) C(7)-N(2)-C(10) C ( 1 0 ) - N ( 2 ) - C ( l l ) N ( l ) - C ( l ) - C ( 6 ) C ( l ) - C ( 2 ) - C ( 3 ) C(3) -C(4) -C(5) C(5) -C(4) -C(7) C ( l ) - C ( 6 ) - C ( 5 ) N(2) -C(7) -C(8) C(7) -C(8) -C(9) 0 (3 ) -C(9 ) -C(10) 0 (4 ) -C(10) -N(2) N(2)-C(10)-C(9) C ( l l ) - C ( 1 2 ) - C ( 1 3 )

117 .9 (2 ) 108 .2 (2 ) 121 .4 (2) 118 .2 (2 ) 118 .0 (2 ) 119 ,5 (2 ) 121 .6 (2 ) 118 .1 (2 ) 112 .5 (2 ) 108 .1 (2 ) 122 .3 (2 ) 126 .8 (2 ) 106 .3(2) 111 .0 (2 )

Table A. 4.

0 ( 1 ) 0 ( 2 ) 0 ( 3 ) 0 ( 4 ) N ( l ) N(2) C ( l ) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C ( l l ) C(12) C(13)

The a n i s o 2 2 -27r (h a*

Anisotropic displacement coefi

U, 11

47(1) 50(1) 31(1) 33(1) 35(1) 21(1) 28(1) 25(1) 24(1) 21(1) 26(1) 30(1) 22(1) 22(1) 26(1) 27(1) 21(1) 32(1) 47(2)

t r o p i c d i s p l

\ y ••• ^

u 22

34(1) 58(1) 26(1) 26(1) 24(1) 22(1) 20(1) 26(1) 23(1) 19(1) 22(1) 19(1) 16(1) 26(1) 18(1) 13(1) 25(1) 29(1) 52(2)

acement

u 33

36(1) 24(1) 19(1) 25(1) 25(1) 19(1) 20(1) 25(1) 25(1) 20(1) 21(1) 24(1) 23(1) 23(1) 21(1) 22(1) 23(1) 24(1) 46(2)

f a c t o r exp

2hka*b*U^2)

icient (A^ xl

u, „ 12

4(1) -15(1)

-3 (1 ) -4 (1 ) 4(1) 1(1) 3(1)

-2 (1) -2 (1) 2(1)

-4 (1 ) -5 (1 ) -3 (1) -3 (1 ) -3 (1 ) -5 (1 )

1(1) 3(1)

25(1)

onent t akes

03)

U „ 13

26(1) 8(1) 0(1)

14(1) 14(1)

7(1) 9(1)

10(1) 8(1) 6(1) 6(1) 7(1) 8(1) 5(1) 4(1) 7(1) 5(1) 9(1)

28(1)

t he form:

u„. 23

1(1) - 8 ( 1 ) 0 (1 )

-3 (1 ) 2 (1) 0 (1 ) 2 (1) 1 (1)

-1 (1 ) 1(1) 0 (1 )

-3 (1 ) -2 (1 ) -2 (1 ) 0 (1 ) 0 (1 ) 2 (1 ) 3 (1)

21(1)

186

Table A. 5. H-Atom coordinates (x 10 ) and isotropic displacement o

coefficients (A^ xlO^)

H(2) H(3) H(5) H(6) H(8) H(llA) H(llB) H(12A) H(12B) H(13A) H(13B) H(13C)

X

6133 5859 8419 8604 5106 9344 9420 8442 8494 10117 10580 10375

y

217 112 2683 2799 1487 1220 791

-1014 -614 -1914 -572 -1187

z

3042 1590 1933 3200 380 1459 587 760 1554 1805 1998 1234

U

50 50 50 50 50 50 50 50 50 50 50 50

187

APPENDIX B

SUPPLEMENTAL MATERIALS FOR THE AB INITIO CALCULATIONS

188

Supporting Information related to Chapter III

Table B.l. Absolute Energies (Hartrees) of Conformations and Reactions of 1, Structures Optimized at the MP2/6-31G** Level

Structure MP2/6-31G**^

H2O 16 17 3a 3a'

CH2O 18 4a

anti-Z-1 syn-Z-1 anti-£;-l syn-E-1

15 5a 19 6a 6a' 20

ZPE^ MP3/6-31G**^ MP4(SDQ)/6-31G*^

Addition of Water to anti-Z-1

-76.21979 -321.57624 -321.57204 -321.62901 -321.63435

17.7

51.1 51.6 54.5 54.5

-76.22609 -321.58932 -321.57934 -321.64578 -321.65116

-76.22848

-321.60775 -321.59841 -321.66087 -321.66593

Addition of formaldehyde to anti-Z-1

-114.18350 -359.52074 -359.59848

-245.34319 -245.33967 -245.34295 -245.34210 -245.29339 ^245.33143 -245.26248 -245.33359 -245.31669 -245.26277

17.2

55.1 59.3

-114.18972

-359.52725 -359.61723

C3N3NO Isomers

35.2 35.1 35.2 35.2 33.2 35.8 31.9 34.6 33.4 31.5

-245.35156 -245.34999 -245.35195 -245.35084 -245.30143 -245.33279 -245.25773 -245.34415 -245.32460 -245.25644

-114.19818 -359.55307 -359.63441

-245.36759 -245.36423 -245.36759 -245.36685 -245.31749 -245.34799 -245.27513 -245.35901 -245.33917 -245.27671

a Calculated using the frozen core approximation, b Zero-point vibrational

energy in kcal/mol.

189

Table B.2. Absolute Energies in Hartrees of Stationary Points in the Addition of Formylketene and Ammonia at the MP2/6-31G* Optimized Geometry.

Structure RHF/6-31G* ZPEa,b freqa,c MP2/6-31G* MP3/6-31G

fket -264.45735 N H 3 -56.184356 min -320.648625 TS -320.644345 P -320.678148

27.2 22.2 53.7 51.5 54.6

144.9 -265.17785 -265.17507 1163.6 -56.354212 -56.365954 101.9 -321.555804 -321.562773 973.3i -321.554557 -321.561859 119.4 -321.571686 -321.587408

* MP4(SDQ)

-265.19555 -56.368948

-321.582642 -321.580810 -321.604130

a At the MP2/6-31G* level, b In kcal/mol. c In cm-1.

190

Table B.3. MP2(FC)/6-31G** Optimized Cartesian Coordinates, Vibrational Frequencies (cm-i) and IR Intensities (km/mol)

anti-Z-1 imidoylketene 8 C 0 . 0 0 0 0 . 9 5 4 0 . 0 0 0 C 1 . 0 7 9 0 . 1 6 8 0 . 0 0 0 C - 1 . 3 2 2 0 . 3 4 4 0 . 0 0 0 H 0 . 1 5 5 2 . 0 2 0 0 . 0 0 0 0 2 . 0 3 0 - 0 . 5 1 9 0 . 0 0 0 H - 2 . 1 4 8 1 . 0 5 9 0 . 0 0 0 N - 1 . 4 7 4 - 0 . 9 3 7 0 . 0 0 0 H - 2 . 4 6 8 - 1 . 1 6 2 0 . 0 0 0

A' A" A' Frequencies 149.4590 162.3345 451.0418 IR Inten 0.4833 23.6618 19.5698

A" A" A' Frequencies -- 491.6120 546.3739 756.3615 IR Inten -- 76.0586 21.3513 29.4271

A" A' A" Frequencies -- 793.1592 995.4442 1087.2711 IR Inten — 35.4149 21.8773 8.4312

A' A' A' Frequencies -- 1141.7093 1224.5079 1427.4909 IR Inten -- 2.5393 57.0584 35.2334

A' A' A' Frequencies -- 1468.4783 1682.8077 2228.7989 IR Inten -- 64.9186 116.5747 552.3963

A' A' A' Frequencies -- 3146.6599 3325.0907 3564.9921 IR Inten -- 58.0287 9.9406 0.4018

syn-Z-1 imidoylketene 8 C 0 . 0 0 3 0 . 9 3 9 0 . 0 0 0 C - 1 . 0 9 4 0 . 1 8 4 0 . 0 0 0 C 1 . 3 4 4 0 . 3 4 3 0 . 0 0 0 H - 0 . 1 3 8 2 . 0 0 9 0 . 0 0 0 0 - 2 . 0 4 2 - 0 . 5 1 4 0 . 0 0 0 H 2 . 1 4 5 1 . 0 7 9 0 . 0 0 1 N 1 . 7 0 3 - 0 . 8 9 4 0 . 0 0 0 H 0 . 8 8 5 - 1 . 5 1 1 - 0 . 0 0 1

A" A' A' Frequencies — 123.5024 166.6009 469.6684

0.0180 7.8384 3.8937 A" A" A'

Frequencies -- 521.8659 542.8811 620.3924 IR Inten -- 27.0456 12.2232 5.0526

IR Inten

191

Table B.3 Continued

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

A" 813.3520 42.6015 A'

1145.2373 1.2855 A'

1468.2013 18.1819 A'

3190.9352 22.5838

A' A" 1075.0663 1133.2190

15.0617 57.0822 A' A'

1275.9569 1380.7179 172.4126 6.6287 A' A'

1680.9161 2221.1055 158.5086 642.4605 A' A'

3293.2121 3506.4359 8.6040 5.2296

anti-E-1 imidoylketene 8 C C C H 0 H N H

0 1

• 1

-0 2 •0

-2 -2

015 273 107 156 384 851 313 963

Frequencies --IR Inten Frequencies --IR Inten Frequencies --IR Inten Frequencies --IR Inten Frequencies -• IR Inten Frequencies --IR Inten

0.562 0.128

-0.362 1.629

-0.263 -1.426 0.090

-0.698

132 7

513 28 806 23

1128 10

1457 10

3123 39

0.000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000

6929 5416 5287 6912 9942 0321 6137 4236 1579 ,1945 ,9106 ,3683

168. 8.

574. 86.

1061. 98.

1296. 18.

1691. 162.

3304. 19

5867 8972 9117 .3428 .3250 .0741 .3807 .3026 .1783 .8828 .0669 .3155

474 21 625

4 1094

6 1374

25 2222 643 3543

0

1930 5832 2867 0358 0240 2246 1991 6319 5512 ,4430 ,9450 ,6289

syn-E-1 imidoylketene

8 C C C H O H

0 . 0 0 0 1 . 2 6 7 1 . 1 0 1 0 . 1 7 3 2 . 3 7 9 0 . 8 1 6

0 . 5 6 0 0 . 1 4 7

- 0 . 4 0 1 1 . 6 2 6

- 0 . 2 3 6 - 1 . 4 5 3

0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0

192

Table B.3 Continued

N -2.361 H -2.506

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

-0.142 0 0.871 0

A" 123.5024 0.0180 A"

521.8659 27.0456 A"

813.3520 42.6015 A'

1145.2373 1.2855 A'

1468.2013 18.1819 A'

3190.9352 22.5838

000 000

A' 166.

7. A'

542. 12. A'

1075. 15. A

1275. 172. A

1680. 158. A

3293. 8

6009 8384

T

8811 2232

0663 0617

9569 4126

9161 5086

2121 6040

A' 469. 3. A'

620. 5. A'

1133. 57. A

1380. 6. A

2221. 642. A

3506 5

6684 8937

3924 0526

1

2190 0822

7179 6287

1055 4605

4359 2296

3a syn-Z-3-amino-2-propenoic acid 11 0 2.187 -0.374 -0.002 C 1.000 -0.080 0.000 C -0.111 -1.014 0.000 C -1.435 -0.702 0-009 N -2.016 0.526 -0.057 H 0.169 -2.054 0.005 H -2.145 -1.521 0.024 H -2.982 0.609 0.201 0 0.604 1.246 0.007 H -1.427 1.334 0.063 H 1.438 1.744 0.011

Frequencies — 90.4653 249.4761 288.3800 IR Inten — 0.3827 34.3931 93.8401 Frequencies -- 367.1462 390.2442 550.5062 IR Inten -- 194.1044 9.7286 21.1560 Frequencies -- 581.6889 613.5689 713.7565 IR Inten — 136.6798 9.8355 16.9540 Frequencies — 732.8572 781.4589 885.0750 IR Inten — 10.2288 80.7253 25.6639 Frequencies — 987.7833 1094.9452 1162.2495 IR Inten — 10.8328 79.0512 75.7998 Frequencies -- 1231.9628 1355.5448 1386.8030 IR Inten -- 109.0316 62.9988 71.4830 Frequencies — 1496.2549 1665.0695 1759.0309 IR Inten — 45.7926 20.7434 184.1857

193

Table B.3 Continued

Frequencies -- 1839.4968 3255.9504 3324 1029 IR Inten — 543.4296 11.4026 1.2806 Frequencies — 3676.9942 3818.3366 3826.7150 IR Inten — 67.5161 101.0571 51.1952

3a' anti-Z-3-amino-2-propenoic acid 11 0 - 0 . 6 1 7 1.290 0 . 0 0 3 C - 0 - 8 5 5 0 .077 - 0 . 0 0 1 C 0 . 1 2 2 - 0 . 9 8 7 - 0 . 0 0 6 C 1 .456 - 0 . 7 1 0 0 .008 N 2 . 0 0 9 0 . 5 2 3 - 0 . 0 3 6 H - 0 . 2 1 5 - 2 . 0 1 0 - 0 . 0 0 2 H 2 . 1 6 6 - 1 . 5 2 9 0 .024 H 2 . 9 8 9 0 . 6 4 1 0 .142 0 - 2 . 1 3 8 - 0 . 3 8 5 0 . 0 0 3 H 1.382 1 .313 0 . 0 3 3 H - 2 . 6 8 9 0 .414 0 .008

Frequencies — 116.0913 191.6368 255.2341 IR Inten -- 3.5514 199.5469 27.6289 Frequencies — 367.1067 399.4856 540.2108 IR Inten -- 38.0295 12.0780 27.2798 Frequencies — 604.7138 671.6397 731.4131 IR Inten -- 136.9526 22.9739 12.6194 Frequencies -- 744.2710 764.3620 953.0583 IR Inten -- 48.8302 21.6953 3.7609 Frequencies -- 990.8186 1118.2085 1167.4496 IR Inten -- 14.7978 126.0111 211.6714 Frequencies -- 1215.0537 1363.9934 1365.5799 IR Inten -- 156.3623 27.5836 77.8511 Frequencies — 1519.5673 1636.1574 1756.1096 IR Inten -- 106.7874 118.0410 341.4277 Frequencies -- 1789.4244 3260.4377 3332.5471 IR Inten — 220.0217 11.2803 1.1196 Frequencies -- 3627.2794 3821.5480 3825.6196 IR Inten -- 66.2243 115.4594 61.3252

4a oxazinone 12 0 -2.301 0.015 -0.088 C -1.088 0.018 0.006 C -0.269 1.220 0.222 C 1.053 1.201 -0.075 N 1.733 -0.001 -0.142

194

Table B.3 Continued

H -0.797 2.146 0.383 H 1.639 2.101 -0.218 H 2.325 -0.152 -0.947 C 0.945 -1.106 0.325 H 1.415 -2.048 0.064 H 0.855 -1.010 1.410 0 -0.376 -1.144 -0.232

Frequencies — 148.8626 305.8614 377.4914 IR Inten — 0.8874 2.3005 99.1529 Frequencies -- 455.3483 487.2830 528.5683 IR Inten -- 16.7819 141.4518 47.3617 Frequencies — 620.8349 744.6081 805.7210 IR Inten -- 23.5598 1.7236 73.8542 Frequencies — 822.3962 875.6141 961.0430 IR Inten -- 4.9016 31.0669 6.0172 Frequencies — 1038.1818 1054.7763 1105.7834 IR Inten -- 18.1792 116.4883 23.5859 Frequencies — 1156.3728 1240.7078 1259.2418 IR Inten -- 15.3782 52.3685 37.0941 Frequencies -- 1369.0221 1441.1695 1468.3705 IR Inten -- 39.9457 3.8678 14.6948 Frequencies — 1519.0476 1549.8223 1696.9034 IR Inten -- 120.1799 3.3983 42.2140 Frequencies -- 1835.5382 3128.4189 3251.2836 IR Inten -- 327.6264 41.7860 16.4722 Frequencies — 3264.4622 3326.0605 3670.7932 IR Inten -- 9.8257 0.7037 37.8117

5a 3-amino-l,2-propadien-l-one 8 C - 1 . 0 4 9 0 . 3 8 9 0 .000 N - 2 . 2 8 7 - 0 . 1 4 5 0 .000 C 0 . 0 8 2 - 0 . 3 5 8 0 .000 C 1.348 - 0 . 0 4 0 0 .000 0 2 . 5 3 5 0 . 0 3 8 0 .000 H - 2 . 3 8 8 - 1 . 1 4 7 0 .000 H - 3 . 1 1 1 , 0 . 428 0 .000 H - 1 . 0 5 8 1 .479 0 .000

Frequencies -- 134.6999 154.2492 213.1046 IR Inten -- 0.6395 7.0293 238.6770 Frequencies -- 472.8460 565.7856 584.2375 IR Inten -- 9.7843 12.8563 40.0868 Frequencies — 650.2495 941.6009 975.5282 IR Inten — 5.5485 10.4612 12.7486 Frequencies — 1196.0706 1349.1562 1427.1840 IR Inten — 7.3697 213.4841 37.2737 Frequencies — 1670.0242 1786.7980 2240.2038 IR Inten -- 78.8184 412.0110 1369-7725

195

Table B.3 Continued

Frequencies — 3184.3838 3682.0681 3836 1932 IR Inten — 29.4619 144.1201 66.7643

6a E-formyliminoketene MP2/6-31G** 8 0 2.324000 -0.055466 0.008620 C 1.137620 -0.370395 -0.003689 C 0.042786 0.598478 0.004128 C -1.218237 0.172954 0.015572 N -2.363164 -0.247897 -0.124481 H -2.906922 -0.453885 0.710711 H 0.824857 -1.430036 -0.025421 H 0.259195 1.656713 0.021043

Frequencies -- 147.3295 167.0762 467.3035 IR Inten -- 6.4547 3.3470 38.2598 Frequencies — 489.3333 581.7849 593.1969 IR Inten -- 22.0328 41.1147 38.0909 Frequencies — 865.1130 931.6064 1021.0965 IR Inten -- 72.9461 453.2191 2.7054 Frequencies — 1116.8934 1166.9746 1360.5923 IR Inten -- 36.4196 69.3918 6.9435 Frequencies -- 1477.5126 1756.9356 2127.6229 IR Inten -- 4.2277 266.4987 461.3300 Frequencies -- 3010.5479 3301.2823 3598.2498 IR Inten -- 89.9499 7.4378 53.3293

6a' planar E-formyliminoketene MP2/6-31G** opt 8 0 -2.329252 C -1.166211 C 0.000000 C 1.228557 N 2.300359 H 3.198786 H -0.944018 H -0.097340

Frequencies --IR Inten

Frequencies --IR Inten

0.156768 -0.247111 0.608341 0.055325 -0.460065 -0.883306 -1.332557 1.682841

A" -805.3393 215.4762 A'

425.4490 91.2629

0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000

A" 156.5191 0.0114 A'

499.3328 63.4472

A' 165.

1. A'

511. 0.

0133 3350

1

9731 9207

196

Table B.3 Continued

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

A' 594.5955 10.3437 A'

1123.4447 5.5606 A'

1484.5730 6.4320 A'

2971.2746 118.2462

A" 615 69 A

1182 130 A'

1757. 410. A'

3313.0114 8.0802

7549 8064

1394 7253

1603 0299

A" 1012.

1. A'

1360. 61. A'

2267. 671. A'

3946. 806.

9464 1845

7009 9715

4646 3260

6768 7306

6aTS mp2/6-31G** opt planar syn-anti H transition structure for Z-imidoylketene 8 C C C H 0 H N H

0 1

-1 0 2

-2 -1 -1

000000 081590 331825 125365 009754 143297 549611 711412

0 0 0 2

-0 1

-0 -1

982948 206787 331444 054154 514837 080631 896185 869873

0, 0, 0, 0 0 0 0 0

000000 000000 000000 000000 000000 000000 000000 000000

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

A' -1222.7820

257.4568 A"

407.7510 102.4194 A"

556.7325 0.8278 A"

948.8617 1.3106 A'

1473.4327 2.7276 A'

2992.0873 162.1466

A' 138.3830 1.1001 A'

444.5478 1.4429 A'

779-9736 17.5868 A'

1126.1292 0.6811 A'

1784.9219 219.4508 A'

3317.0109 6.8002

A" 182.5690 0.0896 A"

499.4815 100.7588 A'

944.7354 50.1007 A'

1397.3311 131.0892 A'

2218.6402 560.2578 A'

4021.6874 345.0878

197

Table B.3 Continued

7 imidoylketene«water complex 11 0 -1.669 -1.132 -0.428 C -0.574 -1.112 -0.014 C 0.686 -1.163 0.432 C 1.650 -0.137 0.094 N 1.336 0.946 -0.539 H 0.950 -2.015 1.038 H 2.669 -0.362 0.411 H 2.167 1.516 -0.684 0 -1.258 1.783 0.452 H -0.400 1.679 0.007 H -1.889 1.827 -0.272

Frequencies — 56.5722 94.5318 127.8660 IR Inten -- 8.0073 7.5661 6.3251 Frequencies — 174.3650 213.4392 225.1126 IR Inten -- 31.7701 80.2454 36.1523 Frequencies -- 351.2313 461.4583 489.0632 IR Inten -- 83.4744 9.0593 54.6327 Frequencies -- 543.7464 650.1609 773.6626 IR Inten -- 49.9076 109.7108 59.0530 Frequencies -- 802.9588 993.5427 1083.2152 IR Inten -- 66.4967 19.8533 9-7975 Frequencies -- 1151.5486 1246.6588 1435.0010 IR Inten — 4.9660 57.4791 53.7742 Frequencies — 1481.5329 1683.7129 1708.5605 IR Inten -- 59.5409 156.7221 54.7270 Frequencies — 2230.1587 3159.5152 3317.2945 IR Inten — 562.5910 50.3864 11.3184 Frequencies -- 3576.9029 3727.9909 3973.0690 IR Inten -- 4.3102 242.8888 60-8658

8 transition structure for addition of water to imidoylketene 11 0 2 . 2 3 6 - 0 . 2 6 0 0 .038 C 1 .055 - 0 . 3 4 2 - 0 . 0 0 8 C - 0 . 0 7 3 - 1 . 1 1 8 - 0 . 0 2 6 C - 1 . 4 4 5 - 0 . 7 3 2 0 . 0 0 1 N - 1 . 9 0 2 0 .487 0-045 H 0 . 1 5 7 - 2 . 1 7 4 - 0 . 0 2 4 H - 2 . 1 3 5 - 1 . 5 7 6 - 0 . 0 1 1 H - 2 . 9 1 5 0 . 5 1 9 0 . 0 5 3 0 0 . 3 7 9 1 .475 - 0 . 1 3 4 H - 0 . 6 4 1 1 .356 - 0 . 0 3 4 H 0 . 7 1 0 1.904 0 .667

Frequencies -- -208.5203 106.6870 259.4209 IR Inten -- 91.6570 3.2883 40.5877 Frequencies -- 350.8102 412.5487 415.0815

198

Table B.3 Continued

IR Inten Frequencies --IR Inten Frequencies --IR Inten Frequencies --IR Inten Frequencies --IR Inten Frequencies --IR Inten Frequencies --IR Inten Frequencies --IR Inten

6 467 79

728 74 977 36

1203 31

1509 30

2103 735 3290

0

4586 6911 1843 0235 9845 4420 2759 7111 9944 9289 7441 9874 8851 6266 9215

36 562 15

742 87

1051 5

1305 152

1656 175

2597 785 3624

17

3966 9485 2360 0603 4942 1355 7400 9990 1591 6344 4525 2539 0089 6476 9926

19 627 66

762 29

1176 16

1438 90

1690 121

3172 37

3888 81.

4631 8825 4186 9150 3409 1275 1990 0846 9219 8082 6469 4764 5493 7546 1141

10 transition structure for addition of formaldehyde to imidoylketene 12 0 2 . 3 5 9 0 .050 0 .227 C 1.278 - 0 . 3 7 6 0 . 0 4 6 C 0 . 3 1 5 - 1 . 3 2 5 - 0 . 0 8 7 C - 1 . 1 1 2 - 1 . 2 3 6 - 0 . 1 0 3 N - 1 . 8 3 9 - 0 . 2 1 1 0 .224 H 0 . 7 4 7 - 2 . 3 1 4 - 0 . 1 6 8 H - 1 . 5 9 3 - 2 . 1 7 0 - 0 . 3 9 4 H - 2 . 8 3 2 - 0 . 3 8 6 0 .085 C - 0 . 7 4 1 1.552 0 .228 H - 1 . 6 0 3 2 . 1 6 2 - 0 . 0 6 3 H - 0 . 6 0 0 1.445 1.309 0 0 . 1 7 9 1 .331 - 0 . 5 8 2

Frequencies -- -331.0521 74.4577 148.7986 IR Inten — 54.2438 1.7296 10.5515 Frequencies — 239.9182 271.5478 305.0085 IR Inten -- 103.6801 23.4039 15.7651 Frequencies -- 362.9448 453.7753 578.3906 IR Inten — 7.4854 73.5035 55.4146 Frequencies — 587.0964 725.6868 754.7982 IR Inten — 47.3333 37.8409 24.5697 Frequencies — 839.7382 951.3097 1041.9914 IR Inten -- 9.8735 41.9740 10.2024 Frequencies — 1187.4270 1199.3067 1259.6668 IR Inten — 3.0591 22.0479 47.3433 Frequencies -- 1284.7117 1442.4696 1506.1691 IR Inten — 12.3620 56.2480 21.9081 Frequencies -- 1535.0454 1677.8688 1728.9153 IR Inten — 33.9425 75.7935 214.4996 Frequencies — 2159-3822 3073.0171 3146.8894 IR Inten — 702.8249 75.9513 85.2789 Frequencies -- 3168.2074 3274.1382 3582.6777 IR Inten — 41.0099 2.2038 11.1815

199

Table B.3 Continued

19 transition structure for 1,3-hydrogen migration from 5a to imidoylketene 8 C -1.159 -0.549 0.000 N -2.160 0.312 0.000 C 0.000 0.229 0.000 C 1.293 0.033 0.000 0 2.478 0.001 0.000 H -1.114 1.144 0.000 H -3.134 0.019 0.000 H -1.266 -1.630 0.000

A' A" A' Frequencies — -1940.0915 69.9933 160.7154 IR Inten -- 1416.4144 6.0765 6.0706

A" A" A' Frequencies — 486.9273 599.3718 622.8478 IR Inten -- 3.8557 141.9923 18.3629

A' A" A' Frequencies — 651.3135 955.5352 1008.6241 IR Inten -- 8.1492 6.2625 34.2369

A" A' A' Frequencies — 1078.1202 1143.2530 1349.3206 IR Inten -- 26.1954 23.8572 35.8966

A' A' A' Frequencies -- 1522.3026 1635.8453 1964.1183 IR Inten -- 130.7902 246.6538 32.4632

A' A' A' Frequencies -- 2241.5944 3244.6470 3595.3683 IR Inten -- 1290.3838 20.6847 37.5079

20 TS for 1,3-h shift, imidoylketene to iminoketene 8 0 -2.206169 -0.368626 0.005763 C -1.040815 -0.082088 -0.023647 C -0.048356 0.894079 0.011800 H -0.058104 -1.035339 -0.032228 C 1.006113 -0.024903 0.027118 H -0.062687 1.972702 0.039937 N 2.222542 -0.234998 -0.055203 H 2.710701 -1.065903 0.240979 Frequencies 1047.1113 237.3477 271.7574 IR Inten — 1792.5884 0.9466 2.2662 Frequencies — 397.1961 566.6347 633.0230 IR Inten — 324.4144 42.5150 46.7003 Frequencies -- 674.8484 726.5927 916.0901 IR Inten — 216.2544 121.9801 15.4220 Frequencies -- 1020.9320 1167.2956 1208.2675

200

Table B.3 Continued

IR Inten — 9.1577 24.3390 Frequencies — 1355.0401 1819.1805 IR Inten -- 1.5137 69.6393 Frequencies — 2012.6777 3321.0489 IR Inten — 358.6051 0.0919

13 1982 388

3737 183

4042 1226 1640 1996 9539

12 MP2/6-31G* optimized geometry and vibrational frequencies of the complex between formylketene and ammonia.

0 C C 0 C H H H N H H

2 0

-0 -1 -1

0 0 0

166235 957277 165378 510420 947664

0.032861 -2.261675 -0.573161

507436 906239 906237

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

-0, -0 -1 -0, 0,

-2 -1 1 1 1 1

398666 231424 066950 630642 559558 131906 435732 311335 293121 745709 745708

?A 101.9416 23.3705

?A 350.0952 9.6300 ?A

592.4481 1.0279 ?A

798.6447 65.3899 ?A

1053.9963 8.3516 ?A

1420.6083 288.1661

?A 1637.5745 154.7764

?A 1886.6479 722.9410

?A 3282.3305

0.3044

0 0 •0

0 0 •0

0 •0

0 -0 0

000001 000000 000001 000000 000000 000001 000002 000002 000000 826522 826523

?A 281.7451

9.4679 ?A

435.8634 7.1934 ?A

606.0574 48.4487 ?A

1008.9829 2.9679 ?A

1120.5868 5.0015 ?A

1469.0034 283.0934

?A 1699.5783

89.3330 ?A

2563.5497 496.3877

?A 3504.8615

63.9023

?A 336.1285 43.2164

?A 475.8312 3.1003 ?A

752.9438 47.1330 ?A

1036.6744 12.4222 ?A

1228.2897 35.8308 ?A

1492.8102 76.4358 ?A

1718.8696 45.7964 ?A

3081.7228 79.5164 ?A

3595.8917 66.7378

201

Table B.3 Continued

13 MP2/6-31G* optimized geometry and vibrational frequencies of the transition structure for the cycloaddition of formylketene and ammonia.

0 -2.159621 -0.367413 -0.000001 C -0.951000 -0-189785 0.000000 C 0.147541 -1.082051 0.000001 O 1.476532 -0.656577 0.000000 H 1.897269 0-561265 -0.000001 H -0.071594 -2.142153 0.000001 H 2.253988 -1.428545 0.000000 H 0.750132 1.186358 0.000000 N -0.455133 1.273832 0.000001 H -0.843106 1.743587 0.822479 H -0.843107 1.743587 -0.822478

?A ?A ?A Frequencies — -973.2860 75.4828 311.4931 IR Inten -- 718.3199 22.9216 14.9582

?A ?A ?A Frequencies — 384.9395 450.4869 470.2531 IR Inten -- 4.3895 19.7816 0.9275

?A ?A ?A Frequencies — 615.8971 637.3358 758.1824 IR Inten -- 2.9399 0.0055 80.9359

?A ?A ?A Frequencies — 767.4976 843.0462 1004.9079 IR Inten -- 42.5457 86.2106 0.3054

?A ?A ?A Frequencies -- 1069.4095 1110.0245 1138.2142 IR Inten -- 57.4176 8.8392 3.4966

?A ?A ?A Frequencies -- 1309.1228 1403.8838 1498.5577 IR Inten -- 241.5363 111.8198 85.0440

?A ?A ?A Frequencies -- 1635.8513 1638.0312 1689.8043 IR Inten — 59.6691 81.2405 240.5881

?A ?A ?A Frequencies — 1825.2669 1875.3392 3149.2541 IR Inten — 950.0034 90.9473 46.4646

?A ?A ?A Frequencies — 3292.0850 3494.4954 3588.9972 IR Inten — 0.0536 41.4928 53.8804

202

Table B.3 Continued

14 MP2/6-31G* optimized geometry and vibrational frequencies of hydroxy-2-propenamide, the product from the cycloaddition of formylketene and ammonia.

3-

O c c 0 c H H H N H H

-2. -0. 0, 1, 1

-0 2 1

-0 -0 -1

070827 966820 180456 469604 944681 042445 276931 167331 679452 211779 524150

-0. -0. -1, -0, 0

-2 -1 1 1 1 1

489313 110023 000973 644536 566567 041136 362277 150125 267005 474980 824433

•0. 0. 0. 0, • 0 ,

0 0 -0 0 1 0

338295 039485 269591 065111 300915 473594 178298 469693 213340 093794 099185

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

?A 119.3998 8.7960 ?A

419.5557 4.9008 ?A

666.3035 29.6339 ?A

845.1990 134.7397

?A 996.2290 33.7606 ?A

1286.5114 183.1796

?A 1472.8825

66.6228 ?A

1812.3601 294.0329

?A 3520.3957 167.4553

?A 252.6064 4.3097 ?A

467.7762 30.3178 ?A

737.7941 22.3407 ?A

876.4910 104.0354

?A 1077.8431

73.2484 ?A

1335.5763 72.6793 ?A

1668.5094 79.9391 ?A

3258.9053 12.3565 ?A

3538.1737 17.3037

?A 311.1976 13.0800 ?A

534.2379 13.4980 ?A

788.2218 18.9196 ?A

929.7060 37.6672 ?A

1158.4996 34.5239 ?A

1465.8726 13.4574 ?A

1710.4029 145.2513

?A 3289.3443

2.2721 ?A

3649-5797 28.9943

203

Table B.3 Continued

NH3 MP2/6-31G-*' optimized geometry and vibrational frequencies of ammonia.

N 0.000000 H -0.939812 H 0.469906 H 0.469906

A' Frequencies --IR Inten

Frequencies --IR Inten

0.116734 -0.272158 -0.272492 -0.272492

A" 1163.6223 186.6045 A'

3502.1359 0.0837

0 0 0

-0

000000 000000 813741 813741

1755 19 A'

3657 0

A' 0761 7389

8426 5933

1755.2643 19.7273 A'

3657.9490 0.5997

15 MP2/6-31G* optimized geometry and vibrational frequencies of the complex for the cycloaddition of imidoylketene and ammonia. 0 0.123245 C 0-000000 C -1.071548 C -0.995172 N 0.106795 H -2.052318 H -1.968146 H -0.079725 H- 1.205321 N 1.390468 H 1.914194 H 1.914194

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

2.222125 1.002717 0.113458

-1.306525 -2.019886

0.573790 -1.810604 -3.021073

-0.848584 0.222732 0.525828

0-000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000

0.000000 0.000000 0.825002

0.525828 -0.825002

A" 105.7638 14.0005 A'

329.2064 35.8919 A"

576.3466 0.8654 A'

737.3623 88.1586 A'

1042.6590 39.4062 A'

1238.0428 15.9762

A" 267.4365 57.4274 A'

432.4381 9.0143 A'

593.7535 65.0889 A"

748.8360 103.1882

A" 1058.7214 0.9948 A'

1239.0989 1.1301

A" 274.7214 5.4910 A'

473.8015 4.3695 A"

723.8369 6.7295 A"

1016.8513 12.1299 A'

1114.8441 3.2755 A'

1425.4186 91.2977

204

Table B.3 Continued

Frequencies --IR Inten

Frequencies — IR Inten

A' 1478.6073 88.9196 A'

1685.0604 61.2908 A'

Frequencies -- 2444.4959 IR Inten -- 571.8424

A' Frequencies — 3503.5381 IR Inten — 52.6830

A' 1526.5174 293.8758

A" 1701.1723 39.5401 A'

3130.9530 49.1433 A'

3561.9978 16.1245

A' 1644.0636 164.5063

A' 1885.0173 798.9134

A' 3276.3111

1.6996 A"

3595.8516 57.2950

16 MP2/6-31G* optimized geometry and vibrational frequencies of the transition structure for the cycloaddition of -imidoylketene and ammonia

0 2.186715 C 0.970185 C -0.115081 C -1.471061 N -1.898805 H 0.129611 H -2.200281 H -0.700132 N 0.484692 H 0.890574 H 0.889930 H -2.908894

-0.351923 -0.194369 -1.083188 -0.696388 0.551327

-2.138049 -1.511788 1.277218 1.289179 1.745267 1.744703 0.658166

• 0 . 0 0 0 3 6 5 0 . 0 0 0 0 0 3 0.000330

-0.000006 -0.000235 0.000579 -0.000067 -0.000140 0-000246 -0.821210 0.822335 -0.000616

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

?A -881.0231 516.9218

?A 301.8494 6.3361

?A 596.3696

3.7406 ?A

720.7445 52.0630

?A 1004.5469

4.2684 ?A

1136.6926 0.0600

?A 86.3287 7.6579 ?A

439.1347 15

625 24

741 87

1069 69

1230 2

5469 ?A 7827 7196 ?A 8758 3643 ?A ,0261 ,2166 ?A .4108 .2958

7 272. 69.

473. 4.

679 29

872 105

1096 4

1333 198

A 2390 5730 'A 2866 9759 ?A 3706 7117 ?A .4780 .7807 ?A .2452 .8147 ?A .6639 .1611

205

Table B.3 Continued

Frequencies — 1411 IR Inten -- 148

Frequencies -- 1631 IR Inten — 92

Frequencies -- 1872 IR Inten — 221

Frequencies — 3493 IR Inten — 35

?A 7670 3700 ?A 8449 7942 ?A 1810 1831 ?A 4844 5342

1519 97

1686 199

3157 37

3589 46

?A 5767 1573 ?A 9023 1814 ?A 5189 3279 ?A 0319 6244

1630 46

1833 995

3283 1

3600 36

?A 0794 1164 ?A 2546 9051 ?A 5977 0813 ?A 7465 3156

17 MP2/6-31G* optimized geometry and vibrational frequencies of the product for the cycloaddition of imidoylketene and ammonia.

0 -2.135651 C -1.006208 C 0-123994 C 1.437638 N 2.002578 H -0.150116 H 2.169074 H 1.386308 N -0.711776 H -0.057835 H -1.558651 H 2.928275

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

-0.456433 -0.078811

-1.001843 -0.699285 0.543023 -2.035620 -1.492602 1.208786 1.283257 1.508376 1.844730

0.513469

?A 112.2161 7.3340 ?A

386.0742 1.2145 ?A

554.0285 85.2497

?A 754.7742 7.4652 ?A

910.8814 14.2955

?A 1144.2585

11.8630 ?A

1378.3314 86.4559

-0.292812 0.019931 0.207752 0.073202 •0.165553 0.381083 0.212713 •0.623943 0.170093 0.914667 0.195316

•0.574433

?A 243.6596 2.6489 ?A

464.4124 37.5855

?A 640.3471 63.1127

?A 794.9727 230.3781

?A 971.3952 3.6617 ?A

1220.8102 7.2027 ?A

1483.8161 54.5955

?A 291.7384 32.0733

?A 533.1754 41.3241

?A 694.6001 44.6599

?A 820.4235 202.8059

?A 1088.3751

35.9021 ?A

1358.0032 56.7094

?A 1663.7654

78.4282

206

Table B.3 Continued

?A ?A ?A Frequencies -- 1689.3870 1743.5805 1803.7501 IR Inten — 36.4595 107.6656 355.7465

?A ?A ?A Frequencies -- 3229.0568 3280.7575 3551.7261 IR Inten -- 10.4530 1.8494 32.8980

?A ?A ?A Frequencies -- 3559.5307 3676.2736 3692.5269 IR Inten -- 28.3522 34.2274 38.3886

207

Supporting Information related to Chapter VII

Table B.4. Absolute Energies (Hartrees) of Conformations Optimized at the MP2/6-31G* Level

Structure

E-2 Z-2

aldehyde 3aTS

3a 4aTS

4a

acetone 3bTS

3b 4bTS

4b

propenal 3cTS

3c 4cTS

4c

RHF/6-31G^

-280.364691 -280.361967 -113.86633 -394.209801 -394.29655 -394.201372 -394.310179

-119.962236 -472.30433 -472.384687 -472.300103 -472.39358

ta 2;pEa MP2/6-31G* MP3/6-31G*

Addition of formaldehyde to E-2

20.90 20.93 18.32 42.23 46.58 41.83 46.82

-281.125998 -281.124579 -114.167747 -395.295396 -395.379695 -395.287637 -395.375512

-281.116605 -281.113884 -114.172854 -395.281696 -395.372563 -395.272456 -395.379398

Addition of acetone to E-2

56.42 79.31 83.71 79.04 83.50

-192.523905 -473.653811 -473.738227 -473.645465 -473.727465

Addition of 2-propenal i

-190.762424 -471.102807 -471.176688 -471.098658 -471.192042

41.71 64.95 68.71 64.38 68.70

-191.311625 -472.437685 -472.513236 -472.43028 -472.509284

-192.547748 -473.658204 -473.746513 -473.650105 -473.748179

to E-2

-191.328896 -472.435402 -472.517317 -472.427807 -472.525204

MP4(SDQ)

-281.138668 -281.137007 -114.181622 -395.314177 -395.396258 -395.304783 -395.401481

-192.579837 -473.694830 -473.774763 -473.687345 -473.774509

-191.341278 -472.471651 -472.545057 -472.464701 -472.551284

^ Optimized at the RHF/6-31G* level.

208

Table B.S. Cartesian Coordinates Optimized at the MP2/6-31G* Level, Vibrational Frequencies and IR Intensities (km/mol) Optimized at the RHF/6-31G* Level

3aTS (nitrosoketene+aldehyde [3+2] TS) 10 nkal32t-mp4.crd O -2.329271 -0.762996 0.000005 6 C -1.163780 -0.707562 0.000001 1 C 0.144743 -1.102164 -0.000001 1 H 0.327922 -2.172814 -0.000005 5 N 1.191342 -0.223451 -0.000001 8 O 2.346117 -0.706511 -0.000002 6 C 0.371262 1.755375 0.000011 1 H 0.907038 2-011096 0.926963 5 H 0.907071 2.011129 -0.926912 5 0 -0.841193 1.474613 -0.000016 6

?A ?A ?A Frequencies -- -455.7123 118.5267 177.4849 IR Inten -- 10.7880 18.0693 8.8552

?A ?A ?A Frequencies -- 221.1933 369.9997 376.9316 IR Inten — 164.7446 28.0255 0.1604

?A ?A ?A Frequencies -- 485.3444 623.8253 632.4604 IR Inten — 16.4804 37.8615 88.1810

?A ?A ?A Frequencies — 682.7071 705.5947 959.0299 IR Inten — 39.3544 85.1191 0.2930

?A ?A ?A Frequencies — 1155.8654 1339.0178 1339.7444 IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

32.4436 298.5722 14.3078 ?A ?A ?A

1379.5792 1491.2179 1577.0953 122.7303 277.7142 90.4099

9A ?A ?A 1780.8806 1803.3724 2361.4117

11.5994 916.7869 1188.2124 9A ?A ?A

3225 5323 3301.5551 3430.4136 50.8167 68.0805 11.3094

3a (nitrosoketene+aldehyde [3+2]) 10 nkal32-mp4.crd O 2.357634 -0.496358 -0.000021 6 C 1.187212 -0.195294 -0.000018 1 C -0.002802 -1.030599 -0.000037 1 H -0.064514 -2.108383 -0.000057 5

209

Table B.S Continued

N -1.083291 -0.254848 0.000010 8 0 -2.302558 -0.527957 0.000034 6 C -0.649270 1.171826 0.000019 1 H -1.041646 1.644326 -0.902458 5 H -1.041632 1.644318 0.902508 5 O 0.759921 1.140325 0.000006 6

?A ?A ?A Frequencies — 194.7372 240.0765 432 8970 IR Inten — 7.1173 24.0491 32.5163

?A ?A ?A

4aTS (nitrosoketene+aldehyde [4+2] TS) 10 nkal42t-mp4.crd 0 -2.090495 C -1.155841 C -0.264589 H -0.633225 N 1.040842 0 1.433070 C 0.844052 H 1.863651 H 0.597724 0 -0.049547

Frequencies --IR Inten

0.153562 -0.288947 -1.249057 -1.977158 -1.284441 -0.376553 1.450508 1.675802 1.715781 1.235696

?A 485.8459 33.8566

-0.550093 -0.010008 0.471220 1.184643 0.137796 -0.691324 -0.070979 0.259005 -1.105664 0.785922

6 1 1 5 8 6 1 5 5 6

?A 66.2483 9.1320

?A 917.6750 80.2512

Frequencies — 590.4825 597.2176 686.8857 IR Inten — 6.3167 0.5720 44 0222

?A ?A Frequencies — 767.7457 794.8936 IR Inten — 7.9000 7^2713

'?A ?A ?A Frequencies — 989.1553 1036.6604 1225.8821 IR Inten — 32.6553 12.0138 7.2810

?A ?A ?A Frequencies — 1262.5458 1281.1869 1329 4999 IR Inten — 153.7769 121.5750 0 0008

?A ?A ?A Frequencies -- 1445.8644 1517.0400 1541 7948 IR Inten — 89.0331 285.2593 35.4286

?A ?A ?A Frequencies -- 1669.2905 1788.1807 2096.3486 IR Inten — 1.9309 621.2653 635.7668

?A ?A ?A Frequencies — 3306.4333 3376.8909 3494.1877 IR Inten — 9.3657 5.6998 14.0036

?A 167.6609 27.3563

210

Table B.S Continued

?A ?A ?A Frequencies -- 263.8896 340.6332 391.9242 IR Inten -- 197.7669 14.8604 10.1913

?A ?A ?A Frequencies — 416.3598 490.3047 730.0560 IR Inten -- 1.9624 81.3285 41.5710

?A ?A ?A Frequencies — 756.8951 779-4870 873.7959 IR Inten -- 93.8838 11.6013 38.6258

?A ?A ?A Frequencies — 1017.0538 1281.8032 1346.2153 IR Inten -- 90.8682 207.4167 57.7519

?A ?A ?A Frequencies — 1363.4802 1472.3925 1622.8980 IR Inten -- 27.1348 567.5797 77.0108

?A ?A ?A Frequencies -- 1698.4462 1844.4328 2287.8186 IR Inten — 261.8170 303.9682 1036.0325

?A ?A ?A Frequencies -- 3269-4258 3367.3397 3409.1461 IR Inten -- 39.9119 37.4012 2.0195

4a (nitrosoketene+aldehyde [4+2]) 10 nkal42-mp4.crd 0 -2.263460 0.015662 -0.098506 6 C -1.055518 -0.027062 0.013071 1 C -0.213827 1.185922 0.208392 1 H -0.713117 2.124159 0.427993 5 N 1.055759 1.270014 -0.058050 8 0 1.662513 0.034199 -0.333676 6 C 0.998383 -1.026510 0.311343 1 H 1.531237 -1.937481 0.051220 5 H 0.988809 -0.842690 1.393966 5 0 -0.345487 -1.178384 -0.150776 6

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

9A ?A ?A 140 2389 320.3349 431.8068

5 0455 22.8401 11.8992 ^A ?A ?A

490 0045 583.6528 650.2501 7.6980 9.5501 3.9141 9A ?A ?A

833.8154 885.7542 987.1765 11.2114 14.1317 41.1792

?A ?A ?A Frequencies - 1019.5428 1042.4044 1204.9565 IR Inten - 62.6375 9.4796 53.8484

211

Table B.S Continued

Frequencies — IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

?A 1223.7838 167.7939

?A 1437.1566

2.8662 ?A

1677.5603 2.3443 ?A

3249.7805 53.3281

?A 1295.4124 20.7263 ?A

1484.7603 196.5453

?A 1892.3789

0.0444 ?A

3396.6106 16.1925

?A 1387.4966

83.5084 ?A

1605.8410 58.7352 ?A

2078.3443 472.6607

?A 3429.4995

0.1339

3bTS (nitrosoketene+acetone [3+2] TS) 16 nkat32t-mp2.crd 0 -2.712312 C -1.847437 C -1.271229 H -1.945174 N 0.079927 0 0.519238 C 0.983182 0 -0.109917 C 1.747969 C 1.748639 H 2.321380 H 1.053341 H 2.445466 H 2.446241 H 1.054446 H 2.321994

-0.000105 -0.000045 -0.000002 -0.000296

-0.990371 -0.000084 -0.204102 -0.000033 1.040232 0.000032 1.892547 0.000196 1.210874 2.386243

-0.788844 -1.403226

-0.598002 1.285886 -0.597964 -1.285481 0.331229 1.272764

-0.603667 2.127065 -1.436521 1.402144 -1.436445 -1.401389 -0.603645 -2.127017 0.331297 -1.272040

6 1 1 5 8 6 1 6 1 1 5 5 5 5 5 5

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

?A -480.3239 100.4146

?A 153.9023 0.2676 ?A

229-8262 14.2365 ?A

446.9317 0.4704 ?A

558.3963 25.1267

?A 44.9480 3.7280 ?A

175.1339 4.0327 ?A

299.9697 3.0122 ?A

447.3297 7.5277 ?A

579.7450 123.8589

?A 149.1752 105.5903

?A 193.5316 0.9314 ?A

395.7926 32.4842 ?A

551.4441 23.7940 ?A

640.3856 25.8878

212

Table B.S Continued

?A 9 A ?A

Frequencies -- 1381.1416 1493.7009 IR Inten -- 48.8839 301.'8445

Frequencies - 705.7855 742.6364 860.8460 IR Inten — 46.4592 63.5514 6.9793

Frequencies — 987.2815 1061.6662 1131.6757 IR Inten — 2.9802 0.0030 32.7057

'^^ ?A ?A Frequencies — 1196.1826 1226.1179 1364.2288 IR Inten — 28.7080 152.1691 295.6141

?A ?A 'PA 1556.3312

0.2806 ?A 9A 9A

Frequencies — 1564.8979 1599.6114 1606.5502 :R Inten — 46.5598 104.6715 0.0127

?A ?A ?A Frequencies — 1613.0593 1633.3364 1724.9679 IR Inten — 1.2555 6.3130 56.1589

?A ?A ?A Frequencies -- 1762.7869 2289.4956 3210.0440 IR Inten — 983.8505 1149.1316 1.6586

?A ?A ?A Frequencies -- 3216.2178 3290.8312 3296.4888 IR Inten — 12.7977 3.5631 11.2650

?A ?A ?A Frequencies -- 3334.6479 3338.1079 3424.4454 IR Inten -- 7.1173 11.4498 3.8467

3b (nitrosoketene+acetone [3+2]) 16 nkat32-mp2.crd 0 c c H N 0 c 0 c c H H H H H H

-2.798598 -1.607831 -0.891057 -1.295285 0.416816 1.393978 0.656578 -0.655954 1.382217 1.382305 2.337727 0.772924 1.553624 1.553878 0.772995 2.337743

-0.270807 -0.048368 1.214627 2.216353

0.975445 1.758869

-0.509809 -1.066894

-0.878371 -0.878330 -0.351042 -0.598398 -1.956800 -1.956734 -0.598474 -0.350868

0-000000 -0.000015 -0.000022 0.000003

0.000009 0.000032

-0.000004 -0.000038 1.274254

-1.274234 1.314801 2.137104 1.294142

-1.294080 -2.137109 -1.314758

6 1 1 5 8 6 1 6 1 1 5 5 5 5 5 5

213

Table B.S Continued

?A ?A ?A Frequencies — 116.9475 210.1940 232.0639 IR Inten — 0.0915 18.5671 0.9888

"A ?A ?A Frequencies — 267.1484 273.0937 332.4247 IR Inten — 0.4308 0.4383 9.1059

?A ?A ?A Frequencies — 352.2339 450.5895 496.0692 IR Inten — 1.9698 23.0286 7.1766

?A ?A ?A Frequencies — 636.7652 660.8228 705.4098 IR Inten — 9.4824 25.9923 6.8546

?A ?A ?A Frequencies -- 757.1980 803.1140 815.4318 IR Inten -- 8.4120 7.5129 5.1490

?A ?A ?A Frequencies -- 937.4322 1001.5240 1033.4667 IR Inten — 63.6081 19.4700 12.0307

?A ?A ?A Frequencies -- 1041.3543 1122.6888 1145.0871 IR Inten -- 0.0165 0.1908 58.1870

?A ?A ?A Frequencies — . 1244.7471 1375.1513 1390.5975 IR Inten -- 35.2940 19.6685 200.1962

?A ?A ?A Frequencies — 1398.7792 1466.0135 1502.7220 IR Inten -- 100.6954 87.0198 222.1208

?A ?A ?A Frequencies — 1560.4553 1578.0886 1620.1186 IR Inten -- 12.8216 2.7378 0.8410

?A ?A ?A Frequencies -- 1622.8714 1640.8917 1647.1713 IR Inten -- 1.1344 0.6496 8.5573

?A ?A ?A Frequencies -- 1778.6218 2083.8113 3234.7357 IR Inten -- 537.0376 694.0320 13.5102

?A ?A ?A Frequencies -- 3239.3606 3309.1790 3312.8224 IR Inten — 4.2320 9.5351 22.8518

?A ?A ?A Frequencies -- 3331.5994 3337.4861 3489.3771 IR Inten -- 1.6580 8.1070 10.5526

4bTS (nitrosoketene+acetone [4+2] TS) 16 0 C c H

nkar42t-mp4.crd -2.120328 -1.642454 -1.697924 -2.689664

-1.549834 -0.480771 0.900548 1.292259

-0.029614 -0.121294 -0.114012 -0.318786

6 1 1 5

214

Table B.S Continued

N 0 C 0 C c H H H H H H

-0.755567 1 0.407127 1. 1.139740 -0. 0.187236 -0. 1.165838 -0. 2.431232 0. 1.705113 -0. 0.157706 -1. 1.689338 -1. 3.122254 -0. 2.242437 0. 2.890915 0.

.870894 547507 471436 712763 956627 036352 255785 105070 920683 806714 485755 766298

Frequencies IR Inten

Frequencies IR Inten

1.0663

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

?A - 3 2 1 . 1 0 0 8

2 4 2 . 5 4 6 0 ?A

1 1 2 . 7 0 7 4 1 . 3 2 9 9

?A 1 9 0 . 8 4 9 6

3 1 . 8 3 9 1 ?A

3 8 2 . 6 5 3 8 2 3 . 0 8 5 4

?A 5 4 2 . 7 3 8 1

6 8 . 9 0 5 0 ?A

7 7 9 . 3 5 6 0 9 6 . 5 7 2 1

?A 1 0 0 0 . 9 9 7 9

7 . 9 5 7 6 ?A

1 1 9 9 . 4 4 1 7 1 . 5 8 9 9 ?A

1 3 9 8 . 3 1 6 4 5 1 . 2 8 0 7

?A 1 5 6 9 . 0 0 4 7

4 6 . 6 3 4 3 ?A

1 6 1 5 . 9 5 1 3 1 0 . 3 4 6 7

?A 1 8 6 7 . 7 3 0 6

5 3 7 . 6 4 5 1 ?A

3 2 2 4 . 8 6 7 0 3 . 7 2 4 7

0 . 0 9 3 6 6 3 0 . 4 8 2 9 0 5

• 0 . 1 4 4 1 4 8 • 0 . 9 1 6 1 2 3 1 . 2 8 0 0 8 4

• 0 . 7 2 2 3 8 1 1 . 9 1 8 3 5 0 1 . 6 6 7 9 5 9 1 . 3 0 1 2 5 4

• 0 . 8 4 0 4 2 1 • 1 . 6 9 7 2 4 2 • 0 . 0 5 3 5 9 9

6 1 6 1 1 5 5 5 5 5 5

?A 76.3132 5.4641 ?A

136.5952 2.3500

?A 307.2443 20.2964 ?A

409.3024 18.5379 ?A

608.8177 38.2445 ?A

858.3484 10.6202 ?A

1028.8032 1.9676 ?A

1224.1778 26.8573 ?A

1476.7727 609.5474

?A 1595.7296

35.9353 ?A

1628.5328 14.1011 ?A

2179.8929 1014.1920

?A 3292.9558

7.5089

?A 91.2292 15.1813 ?A

184.4067

?A 349.4878 1.1793 ?A

475.8816 17.5179 ?A

757.6506 34.5340 ?A

869.4082 60.3872 ?A

1053.4631 111.8414

?A 1297.5716 211.3914

?A 1549.3283

14.5065 ?A

1602.7901 5.0453 ?A

1728.7158 287.1916

?A 3212.7036

2.3679 ?A

3304.4714 3.7562

215

Table B.S Continued

Frequencies - 3339.0837 3354.9841 3410^8122 IR Inten — 6.0500 4.9982 1.5052

4b (nitrosoketene+acetone [4+2]) 16 nkar42-mp4.crd 0 -2.401437 -1.150043 -0.041680 6 C -1.387847 -0.477943 -0.053642 1 C -1.400837 0.999817 0.068149 1 H -2.342091 1.485894 0.305208 5 N -0.413983 1.788211 -0.226699 8 0 0.779289 1.134468 -0.553479 6 C 0.958020 -0-164831 0.024087 1 0 -0.165570 -1.022779 -0.288457 6 C 1.135032 -0.073214 1.529526 1 C 2.144901 -0.755946 -0.692722 1 H 2.027837 0.515727 1.750406 5 H 0.277199 0.399558 2.011482 5 H 1.252737 -1.079844 1.937272 5 H 2.326319 -1.767117 -0.322004 5 H 1.934617 -0.794381 -1.762619 5 H 3.027393 -0.137786 -0.516314 5

?A ?A ?A Frequencies — 105.0464 174.6427 232.7759 IR Inten -- 2.1176 5.7247 0.0657

?A ?A ?A Frequencies -- 268.4766 316.9035 366.3068 IR Inten — 0.2782 2.3853 0.4618

?A ?A ?A Frequencies -- 387.6586 436.2795 515.2235 IR Inten -- 13.8093 8.9694 13.4446

?A ?A ?A Frequencies -- 539.5205 591.9311 612.0090 IR Inten -- 8.1465 4.0356 8.6701

?A ?A ?A Frequencies -- 753.0511 836.5163 943.3126 IR Inten -- 1.4782 14.6210 18.3530

?A ?A ?A Frequencies — 1004.7509 1026.1333 1032.0818 IR Inten — 53.0207 16.2879 7.3095

?A ?A ?A Frequencies — 1039.1478 1124.4762 1130.8715 IR Inten — 12.1607 0.8946 19.0013

?A ?A ?A Frequencies -- 1146.3259 1298.2934 1366.8738 IR Inten -- 93.7179 81.9523 103.5425

216

Table B.S Continued

?A ?A ?A Frequencies -- 1408.8907 1436.8022 1499.8468 IR Inten -- 31.3131 26.2930 344.9682

?A ?A ?A Frequencies — 1570.2062 1581.3635 1622.4740 IR Inten -- 20.7245 30.6079 0.9618

?A ?A ?A Frequencies -- 1623.1823 1641.9433 1648.1897 IR Inten -- 0.5958 2.5054 6.6028

?A ?A ?A Frequencies -- 1900.7993 2066.2555 3233.2018 IR Inten -- 0.4266 514.0822 9.2987

?A ?A ?A Frequencies — 3239.7659 3307.7267 3310.0994 IR Inten -- 7.0261 19.3024 1.7628

?A ?A ?A Frequencies — 3318.7242 3323.7500 3426.6789 IR Inten -- 26.9406 17.8622 0.2931

3cTS (nitrosoketene+2-propenal [3+2} TS) 14 0 -2.843808 -1.080507 0.037309 C -1.967789 -0.302638 0-002985 C -1.439432 0.964375 -0.060190 H -2.147056 1.784872 -0.145805 N -0.097555 1.201906 -0.012841 0 0.279280 2.397636 -0.041248 C 0.768668 -0.811969 0-345936 0 -0.245673 -1.411227 -0.080901 H 0.841756 -0.507537 1.403316 C 2.020127 -0.765516 -0.417425 H 1.977173 -1.104256 -1.448866 C 3.155962 -0.338813 0.155050 H 3.172000 -0-000211 1.187771 H 4.095407 -0.306067 -0.385948

?A ?A ?A Frequencies — -198.1458 80.0223 126.1605

83.1715 29.6914 30.8922 9A ?A ?A

134 5219 178.6175 277.4848 40.7051 4.3328 48-0127 ?A ?A ?A

313.0223 372.2835 428.5642 IR'lnten — 28.4543 6.2402 0.5498

?A ?A ?A Frequencies — 528.4843 538.9999 654.7106 IR Inten -- 96.7625 127.7409 76.0782

217

IR Inten

Frequencies IR Inten

Frequencies

Table B.S Continued

?A ?A ?A Frequencies -- 708.3848 720.5063 788.6946 IR Inten -- 7.9088 74.9497 52.2186

?A ?A ?A Frequencies -- 809.1706 1027.0554 1105.1096 IR Inten -- 77.4108 36.4160 27.9729

?A ?A ?A Frequencies -- 1132.4375 1175.8382 1196.6353 IR Inten -- 21.7395 40.4758 280.7241

?A ?A ?A Frequencies — 1315.0194 1352.2813 1423.9471 IR Inten — 123.5613 374.5180 2.5928

?A ?A ?A Frequencies — 1494.5295 1514.1946 1584.6813 IR Inten -- 81.5682 176.1063 2.9895

?A ?A ?A Frequencies — 1721.8659 1764.6182 1843.5429 IR Inten -- 743.8950 596-2689 306.7845

?A ?A ?A Frequencies -- 2113.7655 3355.6338 3380.5294 IR Inten -- 1034.2981 3.2670 3.7469

?A ?A ?A Frequencies -- 3409.7293 3413.8004 3445.3393 IR Inten -- 0.2266 0.2074 1.0281

3c (nitrosoketene+2-propenal [3+2]) 14 nkar32-mp2.crd 0 -2.781908 -0.444474 -0.470608 6 C -1.656370 -0.139026 -0.148138 1 C -0.910783 1.085552 -0.379977 1 H -1.240882 1.991051 -0.867434 5 N 0.291705 0.982322 0.180379 8 0 1.224168 1.812809 0.273934 6 C 0.448430 -0.389848 0.752323 1 0 -0.829468 -0.995440 0.583956 6 H 0.654285 -0.265414 1.821063 5 C 1.487690 -1.203345 0.041820 1 H 1.430173 -2.263773 0.277043 5 C 2.402322 -0.730154 -0.810409 1 H 2.472903 0.329428 -1.028046 5 H 3.111516 -1.389775 -1.297241 5

?A ?A ?A 62.2031 134.1493 203.3766 0.1878 0.2279 14.7565 ?A ?A ?A

248.5688 405.5541 417.0260 IR Inten — 6.7150 5.2390 28.9336

Frequencies IR Inten

Frequencies

218

Table B.S Continued

?A 7A ''A Frequencies — 487.4802 601.4187 654.0355 IR Inten — 1.9099 6.7170 9.9136

?A ?A ?A Frequencies -- 684.2414 765.8791 795.0818 IR Inten -- 26.8538 4.8577 6.5977

?A ?A ?A Frequencies -- 810.7887 932.1766 1008.7804 IR Inten -- 17.1216 72.2087 20.1234

?A ?A ?A Frequencies — 1029.4543 1067.9703 1129.8141 IR Inten -- 29.9150 5.7404 17.7190

?A ?A ?A Frequencies — 1139.7692 1213.1047 1253.5911 IR Inten — 42.4171 11.1660 149.5619

?A ?A ?A Frequencies — 1292.7502 1431.3305 1449.6414 IR Inten -- 108.8722 85.0512 54.1077

?A ?A ?A Frequencies -- 1492.5279 1502.4262 1518.4797 IR Inten -- 110.0606 28.8758 176.6215

?A ?A ?A Frequencies -- 1589.7065 1786.4583 1880.4969 IR Inten -- 21.3517 519.3823 3.1143

?A ?A ?A Frequencies -- 2091.4651 3305.8943 3355.1881 IR Inten -- 702.4427 9.6566 4.9656

?A ?A ?A Frequencies -- 3374.9431 3454.9135 3492.1732 IR Inten — 7.2788 2.3973 12.7503

4cTS (nitrosoketene+2-propenal [4+2] TS; 14 0 c c H N 0 C 0 H C H C H H

nkar42t-mp2f.crd 2.308228 1.830097 1.866527 2.844713 0.888530 -0.252223 -0.858285 0.066284

-0.755486 -2.200654 -2.306232 -3.241400 -3.108283 -4.250433

-1.535945 -0-517725 0.841963 1.215311 1.794151 1.497649

-0.592570 -0.930409 -0.699877 -0.305907 -0.192838 -0.220876 -0.331452 -0-029876

-0.436446 -0.098929 0.163631 0.449457 0.125189 -0.349095 -0.056941 0.716615

-1.146598 0.447629 1.522680

-0.395384 -1.467106 -0.043379

6 1 1 5 8 6 1 6 5 1 5 1 5 5

219

Table B.S Continued

^A 9A ?A Frequencies — -331.7365 57.3256 69.3701 IR Inten — 290.6900 3.4526 12.6833

?A ?A ?A Frequencies — 107.8610 135.0598 300.5192 IR Inten — 14.2444 2.0763 20.0537

?A ?A ?A Frequencies — 308.7474 340.7261 365.6453 IR Inten -- 50.4568 3.1426 17.0897

?A ?A ?A Frequencies — 424.2793 490.7064 643.8538 IR Inten -- 0.4830 174.0876 25.0894

?A ?A ?A Frequencies -- 700.2504 755.6653 787.0091 IR Inten -- 27.5915 33.8076 83.2890

?A ?A ?A Frequencies — 869.6036 1015.8263 1052.7758 IR Inten -- 77.1365 21.4960 124.1255

?A ?A ?A Frequencies — 1112.7358 1145.1837 1164.7235 IR Inten — 50.6803 31.0983 16.7532

?A ?A ?A Frequencies — 1294.0242 1305.5680 1422.4371 IR Inten -- 237.3770 90.7464 3.8431

?A ?A ?A Frequencies -- 1479.1493 1523.9238 1595.4296 IR Inten -- 557.9454 74.6789 2.3977

?A ?A ?A Frequencies -- 1738.1466 1823.6485 1875.6145 IR Inten -- 319.7039 214.9922 705.0146

?A ?A ?A Frequencies -- 2183.9337 3335.3337 3350.9801 IR Inten -- 1085.7242 10.8763 6.3805

?A ?A ?A Frequencies -- 3404.0919 3409.7503 3441.0745 IR Inten -- 0.1068 1.7999 3.3230

4c (nitrosoketene+2-propenal [4+2]) 14 0 c c H N 0 c 0 H

nkaR42-mp2.crd -2.586612 -1.578156 -1.592954 -2.551033 -0.582923 0.636315 0-669450 -0.331136 0.425907

-1.147869 -0.496053 0.978614 1.463906 1.773064

1.105342 -0.149710 -1.035892 0.011136

-0.215828 -0.034302 0.170393 0.327723

-0.021516 -0.223177 0.422172 -0.119166 1.485456

6 1 1 5 8 6 1 6 5

220

Table B.S Continued

C 1.996221 -0.794782 0.218817 1 H 2.030416 -1.847301 0.488532 5 C 3.069780 -0.147850 -0.244364 1 H 3.020844 0.901359 -0.512081 5 H 4.019743 -0.654512 -0-369944 5

?A ?A ?A Frequencies -- 69.7592 141.0851 181.3391 IR Inten -- 0.1413 4.6167 5.0680

?A ?A ?A Frequencies — 223.7334 383.1264 421.3919 IR Inten -- 0.7756 5.2519 17.0453

?A ?A ?A Frequencies — 510.1506 569.0076 602.1376 IR Inten -- 7.8419 6.7460 2.3078

?A ?A ?A Frequencies — 627.8071 736.2644 830.7739 IR Inten -- 11.4063 2.2763 5.1556

?A ?A ?A Frequencies -- 912.1390 1022.8589 1029.3303 IR Inten — 31.4175 29.6981 50.3678

?A ?A ?A Frequencies — 1066.0669 1108.5040 1121.9365 IR Inten — 7.7725 15.8400 51.6513

?A ?A ?A Frequencies — 1131.9806 1141.9328 1222.2306 IR Inten -- 33.6447 20.8978 228.4414

?A ?A ?A Frequencies -- 1273.4109 1406.3440 1440.8068 IR Inten -- 22.1802 46.0360 5.2805

?A ?A ?A Frequencies -- 1482.1478 1540.4467 1571.6979 IR Inten -- 234.7157 20.8906 91.5622

?A ?A ?A Frequencies -- 1600.9161 1888.2062 1896.9361 IR Inten -- 107.5973 0.6551 0.0144

?A ?A ?A Frequencies -- 2074.3758 3221.7707 3355.3256 IR Inten — 526.1148 46.4170 5.2792

?A ?A ?A Frequencies — 3377.2042 3429.0719 3443.1919 IR Inten -- 4.4497 0.1696 6.9310

221

Supporting Information related to Chanter IX

Table B.O. Absolute Energies (Hartrees) for the Decarbonylation of Furandione, Optimized at the MP2/6-31G* Level, unless otherwise indicated

Level of Theory

RHF/6-31G*«

MP2/6-31G*b

ZPE^

RHF/D95**

MP2/D9S**b

MP3/D9S**b

-377.196057

-378.215794

34.8

-377.269596

-378.292657

-378.294764

ITS

MP4(SDQ)/D9S**b -378.317194

MP4(SDTQ)/D95**b.378.363643

•377.143013

-378.176027

32.1

•377.214053

•378.252206

•378.238694

•378.272653

•378.328820

-264.457349

-265.177850

27.2

-264.506684

-265.233975

-265.233924

-265.253355

-265.287128

CO

-112.737877

-113.021215

3.0

-112.756509

-113.040167

-113.037268

-113.049375

-113.062295

3 RHF/6-31G* geometry optimization. ^ Frozen core approximation. ^ Zero-point vibrational energy in kcal/mol.

222

Table B.7. Absolute Energies (Hartrees) for the Decarbonylation of Pyrroledione, Optimized at the MP2/6-31G* level, unless otherwise indicated

Level of Theory

RHF/6-31G*a

MP2/6-31G*b

ZPE<

RHF/D95**

MP2/D95**b

MP3/D95**b

-357.37448

-358.379797

42.6

-357.445371

-358.458509

-359.467114

MP4(SDQ)/D95**b -358.486965

MP4(SDTQ)/D95**b.358.S32697

3TS

•357.29740

•358.31456

39.5

•357.365031

•358.392552

•358.389859

•358.418539

•358.472985

3TS'

-358.314870

39.7

-358.363950

-358.392649

-358.389755

-358.418113

-358.472787

-244.611097

-245.31769

35.1

-244.656532

-245.375025

-245.385289

-245.400397

-245.433178

^ RHF/6-31G* geometry optimization. ^ Frozen core approximation. ^ Zero-point vibrational energy in kcal/mol. ^ The transition state was planar at the RHF/6-31G* level.

223

Table B.8. Cartesian coordinates, Vibrational Frequencies and IR Intensities (km/mol) Optimized at the MP2/6-31G* Level

1 Furandione

0 1.992556 C 0.771730 C -0.271393 H -0.133762 C 0.000000 0 -1.367253 C -1.446238 H -2.462285 0 0.408630

Frequencies --IR Inten

Frequencies — IR Inten

Frequencies --IR Inten

Frequencies — IR Inten

Frequencies — IR Inten

Frequencies --IR Inten

Frequencies — IR Inten

-0.564022 -0.489335 -1.505871 -2.577526 0.857334 0.537106

-0.843544 -1.219278 1.987578

A" 148.9546 1.0869 A"

494.4296 38.2726

A" 749.1488 24.6100 A'

800.3426 7.0136 A'

1076.6133 52.1668

A' 1399.4124 29.6593

A' 1879.1466 120.2289

0.000000 0.000000 0.000000 0.000000

0.000000 o.oooooc 0.000000 0.000000 0.000000

A" 313.3706 0.0109 A'

567.9703 2.2774 A'

759.0941 6.5257 A"

922.2940 2.9885 A'

1195.4094 64.3597

A' 1651.5302 69.6634

A' 3300.5887

2.9796

321.4259 4.3959 A'

608.3804 11.9743

792.5213 13.7477 A'

954.7922 88.4045

T I r-i

x262.4910 168.9961

A' 178^.8873 143.2318

A' 3331.3146

2.7243

ITS Furandione decarbonylation transition state

0 c c H C 0 C H 0

2.235395 1.074087 0.088498 0.402547 0.000000 -1.799082 -1.298394 -1.988093 -0.136263

-0.232799 -0.507888 -1.458114 -2.494685 1.116450 0.018268

-1.133553 -1.991744 2.262664

0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000

224

Table B.8 Continued

A' A" A' Frequencies — -351.4636 91.3388 167.7514 IR Inten — 58.7440 6.4182 12.2367

A" A" A' Frequencies — 193.0822 277.2026 387.2730

IR Inten -- 4.3645 14.9789 4.1965 A' A' A"

Frequencies — 413.2859 490.9199 621.7527 IR Inten — 79.4230 21.5856 23.1693

A" A' A" Frequencies -- 678.3331 806.7760 1013.8763

IR Inten — 35.3930 73.0728 0.4996 A' A' A'

Frequencies — 1020.2692 1166.6948 1435.1995 IR Inten -- 29.7323 23.0314 64.3424

A' A' A' Frequencies — 1484.2754 1662.2551 2055.8883 IR Inten — 89.9136 271.4411 683.2921

A' A' A' Frequencies -- 2094.4302 3081.4026 3284.8027

IR Inten -- 56.6901 90.6787 3.6220

3 Pyrroledione 0 1.996357 -0.566025 0.000000 C 0.773816 -0.485949 0.000000 C -0.256027 -1.525050 0.000000 H -0.087735 -2.592275 0.000000 C 0.000000 0.871690 0.000000 N -1.336977 0-497758 0.000000 C -1.454888 -0.893719 0.000000 H -2.444681 -1.336436 0.000000 0 0.456069 2.001934 0.000000 H -2.105547 1.155299 0.000000

A" A" A' Frequencies — 99.4670 245.5344 313.7495 IR Inten — 16.7170 37.4785 3.8213

A" A" A' Frequencies — 429.0734 514.6244 554.5967

IR Inten — 82.3680 11.4875 0.2384 A' A" A'

Frequencies -- 627.4725 726.6946 762.1520 IR Inten — 26.1806 61.5185 3.4492

A' A" A" Frequencies — 795.7131 801.0382 909.3546 IR Inten — 6.6250 8.2845 3.5768

225

Table B.8 Continued

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

Frequencies --IR Inten

A' 1071.8038 19.7724

A' 1299.1599 124.9931

A' 1657.5946 57.3688

A' 3282.9301

3.4374

A' 1104.2629 20.2883

A' 1375.7386 39.6241

A' 1776.1792 154.7343

A' 3326.8426 1.3015

A' 1151.1435 27.2522

A' 1450.5105 108.5298

A' 1836.8495 157.7625

A' 3677.9848 96.3406

3TS Non-planar transition state for the decarbonylation of pyrroledione

0 2.142653 C 0.952126 C -0.204659 H -0.086069 C 0.240187 N -1.733332 C -1.508134 H -2.324595 0 0.403258 H -2.700423

-0.697753 -0.736087 -1.457955 -2.526436 1.118107 0.369305

-0.874095 -1.543031 2.263780 0.656298

0.104988 0.007686 -0.070454 -0.208723

-0.070950 0.240837

-0.077659 -0.369297

-0.093425 0.067916

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

Frequencies IR Inten

?A -374.7129 85.6427

?A 188.2030 8.3750 ?A

411.3822 62.6181

?A 641.5539 76.8405

?A 1015.6566 48.1873

?A 1209.5777 35.3681

?A 1662.7138 162.8147

?A 3138.6452 45.9270

?A 81.1707 7.2477 ?A

255.6582 47.2265

?A 481.3498 21.6317

?A 738.5732 64.7449

?A 1041.3502 15.9291

?A 1416.0788 65.1086

?A 2059.6984 642.3010

?A 3272.7745 2.2461

?A 146.4429 8.5330 ?A

383.6190 0-5277 ?A

602.3902 32.2549

?A 761.7731 24.7877

?A 1170.4587 4.5299 ?A

1493.2254 20.5773

?A 2074.2807 122.9079

?A 3501.5588 8.7570

226

Table B.S Continued

3TS' Planar second order saddle point

0 2.249584 -0.218338 0.000000 C 1.090441 -0.512352 0.000000 C 0.115927 -1.466278 0.000000 H 0.460112 -2.493883 0.000000 C 0.000000 1.144275 0.000000 N -1.794421 0.006520 0.000000 C -1.289894 -1.190417 0.000000 H -1.935143 -2.075189 0.000000 0 -0.080403 2.298954 0.000000 H -2.816321 0.027140 0.000000

A' A" A" Frequencies — -362.8688 -93.1595 150.2733 IR Inten — 111.2883 41.5425 15.0450

A' A" A' Frequencies — 152.7446 219.8153 382.2870

IR Inten -- 10.7151 15.0429 0.5409 A' A' A"

Frequencies — 404.4670 494.4285 599.3209 IR Inten — 77.0068 20.5276 37.9186

A" A" A' Frequencies -- 639.0713 732.7800 737.4402

IR Inten -- 49.4533 19.5672 74.3235 A' A" A'

Frequencies -- 1010.3897 1038.9400 1176.4889 IR Inten -- 57.4330 2.3508 5.1606

A' A' A' Frequencies -- 1201.8563 1424.9819 1493.0354 IR Inten — 33.6187 65.8477 22.9321

A' A' A' Frequencies — 1678.2674 2060.9318 2077.9538 IR Inten — 180.7354 663.3823 126.7665

A' A' A' Frequencies — 3137.6679 3273.4296 3516.0001

IR Inten — 47.5330 1.8729 15.3636

227