Indian Journal of Chemistry Vol. 40B, November 2001, pp. 1063-1071

High diastereoselectivity in Hosorni-Sakurai reaction on metal-complexed acyclic enones: Role of out-of-plane coordination of Lewis acidt

Surojit Sur·1, Sunil K Mandal·H, Sambasivam Ganesh·§, Vedavati G Puranikb & Amitabha Sarkara* "Divisions of Organic Chemistry (Synthesis) and Physical Chemistry, National Chemical Laboratory, Pune 411 008, India

E-mail: sarkar@ems. ncl.res.in

Received 24 February 2001; accepted 31 July 2001

Efficient diastereocontrol is achieved in Hosomi-Sakurai reaction of flexible acyclic enones anchored on arene­tricarbonylchromium template. Relative stereochemistry of groups in the products is compared with those obtained by al­lylmagnesium bromide addition followed by an anionic oxy-Cope rearrangement. The results indicate an endo-selective conjugate addition dictated by an out-of-plane bound Lewis acid in the Hosomi-Sakurai reaction, similar to the trend estab­lished earlier for rigid substrate structures.

We recently reported I an unusual , endo-selective, conjugate allylation on 2-arylidene-1-tetralone tricar­bonylchromium complex2 by Hosomi-Sakurai reac­tion3

. In this stereochemically well-defined substrate, the expected in-plane coordination of Lewis acid to the ketone carbonyl group was thought to be pre­vented by two flanking hydrogens, the peri proton of the aromatic ring of tetralone and the l3-olefinic pro­ton, held in a rigid framework. As a result, the Lewis acid was forced to coordinate in an out-of-plane man­ner from the more accessible exo face, which in tum blocked approach of reagent from the same face. The net effect was an endo-selective allylation (Scheme I). The same concept was subsequently ex­ploited to predictably induce endo-selective nucleo­philic additions of organolithium4 and organomagne­sium5 reagents to such substrates in presence of Lewis acids.

In flexible, acyclic analogues, a rotation about the C(O)-alkene bond leading to cisoid (I and II) or tran­soid (III) orientation of the enone (Chart 1) can jeop­ardize diastereoselectivity. It may be noted, however, that the steric inhibition offered by the flanking hy­drogens in I or II (cisoid orientation) would still ad-

tDedicated to Prof. U.R. Ghatak on his 70th birthday . • Division of Organic Chemistry (Synthesis) b Division of Physical Chemistry , Present address: John Hopkins University, Baltimore, Maryland, USA. # Present address: Louisiana State University, Baton Rouge, Lou­isiana, USA. § Present address: Syngene International Pvt. Ltd., Bangalore, India.

versely affect the in-plane approach of Lewis acid, but such a constraint is absent in the transoid structure III.

In this paper, we wish to report that Hosomi­Sakurai reaction on representative acyclic enones an­chored on tricarbonylchromium proceeds with high diastereoselectivity in spite of built-in flexibility of the substrate structure6

• In addition, the results also suggest that the stenc course of this reaction is biased in favour of less common endo-allylation by an out­of-plane-bound Lewis acid to the enone carbonyl, as observed in case of previously reported rigid sub­strates l

.

Results and Discussion The stereochemical course of reaction (exo or endo

attack) on acyclic substrates can be deduced if the reactive conformation (syn or anti orientation prefer­ence) of the substrate and the stereochemistry of the product are known, as shown in Chart 2. The E con­figuration of the enone double bond was established from the proton NMR data (J,roll s = 16 Hz), and the cisoid geometry was ascertained based on the chemi­cal shift of the l3-olefinic proton7 (7.8 ppm). The chemical shift of the aromatic peri proton has been used to determine the orientation of the ketone car­bonyl (syn or anti with respect to the ortho­substituent) . The anti conformation has the carbonyl group oriented in such a way that the peri proton is considerably deshielded by the carbonyl group anisot­ropy (doublet at 6.2 ppm). For the syn conformation, this doublet appears at around 5.7 ppm.

1064

~A' I Cr(COh

II

Ar

INDIAN J. CHEM., SEC. B, NOVEMBER 2001

~ Ar

o ~SiMe3~"'H -:no; \U \\

-7SOC I \ Cr(COh

Scheme I

~ 0 G' ~A'

I R Cr(COh

Chart 1

~ <J'-5~

Ar

deshielded typical Ar

(6.20 ppm) (5 '70~pm)

tently high diastereoselectivity (Scheme IIffable I and Scheme IIlffable II). We recognized that 1,2-addition by allyl magnesium bromide followed by ani­onic oxy-Cope rearrangement9 on an acyclic enone substrate will yield a l,4-adduct which would be iso­meric - if not identical - with respect to the Hosomi­Sakurai product from the same substrate, and used this reaction for structural correlation.

~ H ;/0

~o ~[) I R I R Cr (CO)3 Cr (COh

Anti / Syn

Ex approach Ex approach

Endo approach

o Nu

~~' Cr (COh

Chart 2

In the following discussion, a cisoid enone confor­mation is only considered relevant for discussion of the transition state of Hosomi-Sakurai reaction8

•

We restrict the major part of the discussion to re­actions of substrates 1 and 2, which displayed consis-

For the o-methoxy substrate 1, allylmagnesium bromide afforded a single diastereomer of the 1,2-addition product, Sa, whose structure was determined by X-ray crystallography 10 (Figure 1). The relative stereochemistry of groups in complex Sa established that an exo addition took place since the carbonyl group preferred an anti orientation II (i.e. away from the methoxy group) in complex 1. The complex Sa was subsequently rearranged in presence of KH to produce a single diastereomer of the formal 1,4-adduct, 9a. The crystal structure of this product (Fig­ure 2) confirmed that the rearrangement indeed oc­curred from the same 1t-face as anticipated.

The Hosomi-Sakurai reaction on the same substrate 1, on the other hand, yielded a pair of diastereomeric products, 9a and 9b, inseparable by chromatography. The ratio (9a:9b = 4: 1) was determined from the inte­gration of well-resolved peaks in the proton NMR spectrum. However, the major isomer was isolated in

SUR et al.: HOSOMI-SAKURAI REACTION ON METAL-COMPLEXED ACYCLIC ENONES 1065

o

Ar II

0

Sa - 8a 9a - 12a

+ ~A' ~ HOJ I R

~A' o Cr (CO)3 II

1- 4 ~ ··" "'Ar

Ar = 4-CH3C6H4 I R ~MgBr -78 DC Cr (CO)3 ,

5b - 8b II KH, Et;P, 0 DC

Scheme II

~A< I R Cr(COb

1- 4

Ar = 4-CH3C6H4

III -

III ~SiMe3, TiCI4 , -78 DC

+

9a -12a 9b - 12b

Scheme III

pure form by fractional crystallization from CH2Clr pet ether and its identity with previously described complex 9a was established by comparison of their NMR spectra. While this result can be readily ex­plained in terms of an exo-selective reaction on the anti conformer of 1, the high oxophilicity of TiC14

cannot be completely overlooked. It seems entirely possible that TiCl4 can be involved in a six-membered chelate by simultaneous complexation with the meth­oxy as well as the carbonyl oxygens12. Such an ar­rangement would ensure a syn orientation of the car­bonyl group, and in that case the major product would be formed by an endo-addition. This line of reasoning appears to be consistent with results obtained with 0-

SiMe3 substituted substrate 2 described below. The reactions on the substrate 2 were completely

diastereoselective (Tables I and II) - one and the

same diastereomer was obtained from either reaction sequence. The end product, unfortunately, was a low­melting solid whose crystal structure could not be determined. Therefore, the carbinol 6b was crystal­lized and its crystal structure was determined (Fig­ure 3). Since the Grignard reaction at the benzylic site is usually exo-selective13

, the structure of 6b indicated that the reactive conformation of the substrate had a

• • 14 syn onentatlOn .

Since we have now established that anionic oxy­Cope rearrangement occurs from the same 1t-face (e.g. Sa to 9a), the rearranged product should have the structure represented as lOb, where the stereochemis­try of the new stereogenic center is opposite to that in 9a.

It seems unlikely, however, that a syn-preference would persist in substrate 2 when TiCI4 strongly

1066

Enone R

1 OMe

2 SiMe3

3 Me

4 CHMe2

Enone

1

2

3

4

INDIAN 1. CHEM., SEC. B, NOVEMBER 2001

Table I- Treatment of enones 1-4 with allylmagnesium bromide and KH

Condition

R

OMe

SiMeJ

Me

CHMe2

Figure I

Figure 2

Product Yield (%) Condition Product Yield (%)

Sa 82 ii 9a 87

6b 65 ii lOb 59

7a+7b 87 ii lla 95 (2: 1) lib 81

8a+8b 81 ii 12a 81 (2.4: I) 12b 81

Table II-Treatment of enones 1-4 with allyltrimethylsilane

Condition

iii

iii

iii

iii

Product Yield (%)

9a+9b 85 (4:1)

lOb 68

lla+llb 86 (1:2)

12a+12b 81 (1 :2.4)

Figure 3

complexes with and activates the ketone carbonyl 15 as a prelude to allylation in Hosomi-Sakurai sequence (condition iii, Scheme III). The reactive conformation is more likely to be anti on steric grounds. To sub­stantiate this expectation, we conducted the Grignard reaction in presence of TiC14 , which was expected to disrupt the syn conformation by complexing with the ketone carbonyl. The reaction afforded the diastere­orner lOb - the l,4-addition product in one step, as precedented for cyclic substrates4

,5 (Scheme IV). This experiment established that the carbonyl

group does adopt an anti conformation in presence of

SUR el al.: HOSOMI-SAKURAI REACTION ON METAL-COMPLEXED ACYCLIC ENONES 1067

/TIC4 0

~tJgBr

~ G) Ar -7aoC

Si(Cl1!)3 endo (1,4) attack Cr (OOb

T~' ~ ~tJgBr KH/-7aoC G) ,',0 G) Ar

-7aoC ~ •

I Si(Cl1!)3 I Si(Cl1!)3 I exo (1.2) attack Cr (OOb Cr (OOb Cr(OOb

6b 10b

To.~ 20/ TO.

~ ~ Si~ / G) Ar ° TiC14/-7a C

Si(Cl1!)3

Cr(OOb

Scheme IV

a Lewis acid, and therefore, the postulation of anti­conformation of 2 in presence of TiCl4 is indeed rea­sonable. Yet, if the Hosomi-Sakurai product has the structure lOb, it can only be explained in terms of an endo-allylation on the Lewis acid-bound anti­conformer of 2.

Stereoselectivity was rather modest for o-alkyl sub­stituted substrates 3 and 4, no matter which reaction sequence was employed 16 (Scheme Urrable I and Scheme IIIffable II). However, one trend clearly emerged in spite of poor diastereoselectivity : the major isomer from Grignard/oxy-Cope sequence was always the minor isomer in Hosomi-Sakurai reaction. Overall, the trend is consistent with preferential exo (Grignard) or elldo (Hosomi-Sakurai) addition to the sterically less strained anti conformer of the substrate.

Conclusion Efficient diastereocontrol in allylation (three car­

bons away from arene-chromium template) of a con­formationally flexible enone, is not the only signifi­cant result described in this paper. The stereochemis­try of the major isomer of Hosomi-Sakurai reaction tends to imply that the reaction proceeded by a less­common, endo-selective attack of allylsilane, since the exo-approach was shielded by titanium tetrachlo­ride bound to the ketone carbonyl in an out-of-plane

manner. Since endo-functionalization is rarely ob­served on an arene-chromium complex 17, these results provide a conceivable strategy of reversing normal exo-preference by modulating steric influence of 1t­

bound Lewis acids to carbonyl groups, even in con­formationally labile, acyclic molecules.

Experimental Section All reactions were performed under an inert atmos­

phere of argon, using freshly distilled, degassed sol­vents. Infrared spectra were recorded on a Perkin­Elmer 599B spectrometer in chloroform. 1H (200 MHz) and 13C (50.3 MHz) NMR spectra were re­corded on a Bruker AC 200 spectrometer in CDCh. Chemical shifts are reported in ppm relative to tet­ramethylsilane as internal reference. Elemental analy­ses were carried out on a Carlo-Erba 1100 automatic analyzer by Dr S Y Kulkarni and his group at NCL. Melting points in the Celsius scale were determined in open capillary tubes on a Thermonik Campbell melt­ing point apparatus and are uncorrected The substrate enones and allyltrimethylsilane were prepared fol­lowing standard procedures.

General method for the preparation of eoones 1-4. A solution of p-tolualdehyde (2.64 mmoles) and the ortho-substituted acetophenone chromium tricar­bonyl complex (1.76 mmoles) in ethanol 00 mL) was

1068 INDIAN 1. CHEM., SEC. B, NOVEMBER 2001

cooled in ice salt bath. An ethanolic solution of KOH (1.76 mmole) in 10 mL ethanol was added dropwise via syringe. The reaction was monitored by TLC. Af­ter complete disappearance of starting material the reaction mixture was worked up. Ethanol was re­moved under reduced pressure, washed with water and extracted with dichloromethane. Removal of di­chloromethane provided the enones as orange to red solid products 1-4. The crude products were washed with pet ether (3 x 20 mL) and recrystallized from dichloromethane-pet ether to afford analytically pure complexes.

Complex 1: Red solid (m.p.129 0c). 'H NMR: 2.40 (s, 3H); 2.41 (s, 3H); 5.10 (d, IH, 1=6 Hz); 5.20 (t, IH, 1=7 Hz); 5.65 (t, IH, 1=6 Hz); 5.93 (d, IH, 1=7 Hz); 7.20 (m, 3H); 7.55 (d, 2H, 1=9 Hz); 7.80 (d, IH, J=16 Hz); '3C NMR: 20.6, 21.8, 87.8, 92.0, 95.9, 96.4, 103.0, 110.2, 122.0, 1298.9, 130.0, 131.8, 141.9, 145.6, 190.2, 231.9;IR: 1980, 1920, 1660, 1600 cm·'. Anal. Calcd: C, 64.5; H, 4.33. Found: C,64.85; H,4.62%.

Complex 2: Red solid (m.p.165 0c). 'H NMR: 0.4 (s, 9H); 2.40 (s, 3H); 5.45 (m, 2H); 5.60 (t, IH, 1=6 Hz); 5.75 (d, IH, J=7 Hz); 7.10-7.25 (m, 3H); 7.55 (d, 2H, 1=9 Hz); 7.85 (d, IH, J= 16 Hz); '3C NMR: 0.7, 21.8, 92.9, 93.4, 99.0, 101.3,108.3, l20.2, 128.9, 130.0, 131.8, 142.0, 146.0, 191.4, 232.1;IR: 1980, 1920, 1660,1600 cm·' . Anal. Calcd: C, 6l.38; H, 5.15 Found: C, 6l.1O; H, 5.15%.

Complex 3: Red solid (m.p.127-129 0c). 'H NMR: 2.40 (s, 3H); 3.90 (s, 3H); 5.00 (t, IH, J=6 Hz); 5.10 (d, IH, 1=7Hz); 5.80 (t, IH, 1=6 Hz) ; 6.20 (d, IH, J=7Hz), 7.20 (d, 2H, 1=9Hz); 7.45 (d, 2H, 1=16Hz); 7.55 (d, 2H, 1=9Hz); 7.75 (d, 2H, 1=16Hz); I3C NMR: 21.3 , 55.9, 72.5, 84.2, 92.5, 95 .1, 95 .9, 123.7, 128.4, 129.5, 132.0, 140.9, 143.0, 143.9, 186.8, 231.4; IR: 1980, 1920, 1660, 1600 cm·'. Anal. Calcd: C, 62.00; H = 4.13. Found: C,61.60; H,4.46%.

Complex 4: Red solid (m.p.141 0c) 'H NMR: 1.30 (m, 6H); 2.40 (s, 3H); 3.1 5 (m, 1H); 5.30 (m, 2H); 5.60 (t, IH, J=6Hz); 5.70 (d, IH, J=7Hz); 7.15 (d, IH, J=16Hz) ; 7.25 (d, 2H, J=9Hz); 7.55 (d, 2H, J=9Hz) ; 7.80 (d, IH, J=16Hz); I3C NMR: 21.2, 21.6, 26.7, 29.2, 87.4, 89.1, 93.0, 94.5, 94.8, 105.5, 12.3, 123.1 , 128.9, 131.6, 141.9, 145.7, 190.7, 232.1;IR: 1980, 1920, 1660,1600 cm·'. Anal. Calcd: C, 66.00; H, 5.03 Found: C, 65.79; H, 5%.

General procedure for addition of allylmagne­sium bromide to complexes (1-4)

Allylmagnesium bromide was always freshly pre­pared by dropwise addition of allyl bromide (0.42

mL, 5 mmole) to magnesium turnings (300 mg, 12.5 mmole) activated by iodine, in diethyl ether (5 mL). The reagent (1.2 mmole) was added dropwise to a solution of the complex (1-4, 1 mmole) in anhydrous THF (5 mL) at -78 °C. The color of the solution be­came pale yellow. The course of the reaction was monitored by TLC. On disappearance of all starting material (30 min), the reaction mixture was quenched with water (5 mL) and extracted with dichlo­romethane (3 x 15 mL). Flash column chromatogra­phy (15% ethyl acetate-pet.ether) yielded the product (5-8).

Complex Sa: The reaction of o-methoxy acetophe­none benzylidene 1 (388 mg, 1 mmole) with allyl­magnesium bromide (1.2 mL, 1.2 mmole) afforded the complex alcohol Sa as a yellow crystalline solid (352 mg, 82 %), m.p. 149°C; IR : 3020, 1980, 1920 cm";'H NMR : 2.35 (s, 3H); 2.70 (s, IH); 2.85 (d, 2H); 3.85 (s, 3H); 4.80 (t, IH); 5.00 (d, IH); 5.10-5.25 (m, 2H); 5.60 (t, IH, 1 = 6Hz); 5.75-5.95 (m, IH); 6.20 (d, IH, 1 = 7Hz); 6.75 (s, 2H), 7.15 (d, 2H, 1 = 9Hz); 7.40 (d, 2H, 1 = 9Hz);13C NMR : 21.4,23.6, 26.6, 29.9, 32.4, 45.2, 56.0, 73.2, 74.5, 83.4, 95.3, 96.2, 106.1, 119.5, 125.2, 126.8, 128.1, 129.4, 133.2, 134.2, 134.4, 135.4, 137.6, 141.3,233.3. Anal. Calcd: C, 64.30; H,5.10. Found: C, 64.75; H, 4.46%.

Complex 6b : The reaction of o-trimethylsilyl acetophenone benzylidene complex 2 (430 mg, 1 mmole) with allyl magnesium bromide (1.2 mL, l.2 mmole) afforded the complex alcohol 6b as a yellow crystalline solid (306 mg, 65 %), m.p . 164 °C; IR : 3030, 1960, 1880 cm" ;'H NMR : 0.45 (s, 9H); 2.40 (s, 2H); 2.45 (s, 3H); 2.75 (m, 2H); 5 .. 10 (m, 2H); 5.25 (m, 2H); 5.60 (t, IH, 1 = 6 Hz) ; 5.70-5.95 (m, 2H); 6.40 (d, IH, 1 = 16 Hz); 6.75 (d, JH, 1 = 16 Hz); 7.20 (d, 2H, 1 = 9 Hz); 7.40 (d, 2H, J = 9 Hz);I3C NMR : 3.7, 21.4,49.2, 89.8, 90.0, 102.1, 121.0, 126.1 , 126.9, 129.4, 129.6, 131.3, 132.7, 133.6, 138. 2, 233.4. Anal. Calcd: C 63.54; H, 5.97. Found: C, 63.21; H, 5.90%.

The reaction of o-methylacetophenone-benzyli­dene, 3 (372 mg, 1 mmole) and allylmagnesium bro­mide (1.2 mL, 1.2 mmole) afforded a mixture of alco­hols 7a-b (360 mg, 87 %) in the ratio 2: 1. Chromatog­raphy and crystallization yielded the pure complexes as yellow crystalline solids.

Complex 7a : m.p. 133 °C; IR : 3020, 1980, 191O;'H NMR : 2.25 (s, IH); 2.40 (s, 3H); 2.55 (s, 3H); 2.85 (m, 2H); 5.00 (m, 2H); 5.55 (t, IH, 1 = 6 Hz) ; 5.70-5.95 (m, 2H); 6.50 (d, IH, ] = 16 Hz); 6.80

SUR et al. : HOSOMI-SAKURAI REACTION ON METAL-COMPLEXED ACYCLIC EN ONES 1069

(d, 1H, J = 16 Hz); 7.20 (d, 2H, J = 8 Hz); 7.40 (d, 2H, J = 8Hz); 13C NMR : 21.0,21.1,45.9, 75.3, 87.3, 93.2, 95.9, 96.3, 10.5, 15.3, 120.4, 126.6, 129.3, 130.7, 131.9, 132.5, 133.3, 137.9, 233. Anal. Calcd: C,64.52; H,4.33 . Found: C, 64.27; H, 4.00%.

Complex 7b : m.p. 179°C; IR : 3020, 1980, 1900 cm-' ; 'H NMR : 2.15 (s, 1H); 2.35 (s, 6H); 2.85 (m, 2H); 5.00-5.30 (m, 4H); 5.55 (t, 1H, J = 6 Hz); 5.80-6.00 (m, 2H); 6.35 (d, 1H, J = 16 Hz) ; 6.65 (d, 1H, J = 16 Hz); 7.15 (d, 2H, J = 8 Hz); 7.35 (d, 2H, J = 8Hz); '3C NMR : not recorded. Anal. Calcd: C, 64.52; H, 4.33. Found: C, 64.09; H, 3.98%.

The reaction of o-isopropyl acetophenone benzyl­idene 4 (400 mg, 1 mmole) with allyl magnesium bromide (1.2 rnL, 1.2 mmole) afforded a mixture of product alcohols 8a-b (358 mg, 81 %) in the ratio 2.4: 1. Chromatography and crystallization yielded the pure complexes as yellow crystalline solids.

Complex 8a : m.p. 190 °C; IR : 3030, 1980, 1920 cm-' ;'H NMR : 1.05 (d, 3H); 1.30 (d, 3H); 2.35 (s, 3H); 2.50 (s, 1H); 2.80 (m, 2H); 3.60 (m, 1H); 5.20-5.45 (m, 5H); 5.65 (d, 1H); 5.90 (m, IH); 6.40 (d, 1H, J = 16Hz); 6.65 (d, 1H, J = 16Hz); 7.15 (d, 2H, J = 9Hz); 7.30 (d, 2H, J = 9Hz); I3C NMR : 21.4, 24.3, 26.3, 28.0, 46.2, 91.6, 91.8, 92.0, 92.6, 121.2, 126.7, 129.6, 130.0, 132.3, 133.7, 233.8. Anal. Calcd: C,66.00; H,5.03. Found: C, 66.21; H 5.01 %.

Complex 8b : m.p. 141 °C; IR : 3020, 1980, 1920 cm-' ; 'H NMR : 1.25 (d, 3H); 1.35 (d, 3H); 2.35 (s, 3H); 2.45 (s, 1H); 2_85 (d, 2H); 3.85 (m, 1H); 5.20-5.50 (m, 6H); 5.80 (m, IH); 6.50 (d, 1H, J = 16Hz); 6.80 (d, IH, J = 16Hz); 7.20 (d, 2H, J = 9Hz); 7.40 (d, 2H, J = 9Hz);' 3C NMR : 21.4, 24.2, 26.1, 27.9, 46.7, 90.9, 9l.6, 92, 93.3, 93.8, 117, 120.5, 123.6, 126.9, 129.6, 129.9, 13l.3, 132.1 , 132.9, 133.5, 138.3, 233 .6. Anal. Calcd: C, 66.00; H, 5.03. Found: C, 66.36; H, 5.29%.

General procedure for anionic Oxy-Cope rear­rangement of complexes (Sa, 6b, 7a-b and 8a-b). Potassium hydride (35% dispersion in mineral oil) was transferred to the reaction vessel and washed twice with pet. ether and twice with diethyl ether. All residual solvent was then removed in vacuo. 5 rnL was then transferred to the fl ask. The flask was then cooled to O°C in an ice bath. An ethereal solution of the complex (1 mmole) were then transferred to this solution. Finally 18-crown-6 (5 wt%) was added. The reaction was monitored by TLC and upon consump­tion of the starting material (2.5 hr) it was quenched with saturated NH4Cl solution (5 mL) and extracted

with dichloromethane. Recrystallization from dichlo­romethane-petroleum ether afforded products as red crystalline solids.

Complex 9a: The reaction of alcohol Sa (430 mg, 1 mmole) with KH (40 mg, Immole) at O°C resulted in the complex ketone 9a (370 mg, 87 %) as a red crystalline solid, m.p.166 °C; IR : 1980, 1920, 1680 cm-'; 'H NMR : 2.40 (s, 3H); 2.70 (s, IH); 2.85 (d, 2H, J = 9 Hz), 3.90 (s, 3H); 4.85 (m, IH); 5.00-5.25 (m, 3H); 5.60 (d, IH, J = 6 Hz);5 .80 (m, 1H), 6.20 (d, 1H, J = 7Hz); 6.75 (s, 2H), 7.10 (d, 2H, J = 9 Hz), 7.40 (d, 2H, J = 9 Hz); I3C NMR : 20.7, 40.3, 48.6, 55.7, 72.1, 83.7, 90.8, 95.6, 116.2, 127.2, 128.9, 135.5, 136.4, 140.8, 143.8, 196.1,230.9. Anal. Calcd: C, 64.30; H, 5.10. Found: C, 64.75 ; H, 4.46%.

Complex lOb: The reaction of alcohol6b (118 mg, 0.25 mmole) with KH (10 mg, 1 mmole) at -78°C af­forded the complex ketone lOb (70 mg, 59%) as a red oil. IR : 1980, 1920, 1700 cm-'; 'H NMR : 0.45 (s, 9H); 2.30 (s, 3H); 2.45 (t, 2H, J = 8 Hz); 3.05 (m, 2H); 3.40 (m, IH); 5.00 (m, 2H); 5.45 (m, 3H); 5.60-5.80 (m, 2H); 7.20 (bs, 4H);I3C NMR : 0.47, 20.9, 29.7, 40.3, 40.7, 43.9, 91.7, 93.2, 93.3, 98.2, 116.9, 127.4, 129.2, 136.0, 136.3, 199.6, 231.4. Anal. Calcd: C, 63.54; H, 5.97. Found: C, 63.57; H, 5.83%.

Complex 11a: The reaction of alcohol 7a (200 mg, 0.5 mmole) with KH (20 mg, 0.5 mmole) at O°C af­forded the complex ketone 11a (191 mg, 95%) as a red oil. IR : 1980, 1920, 1690 cm-' ; 'H NMR : 2.25 (s, 3H); 2.35 (s, 3H); 2.45 (m, 2H); 3.10 (d, 2H, J = 7Hz); 3.45 (m, 1H); 5.05 (m, 4H); 5.55-5.80 (m, 2H); 5.80 (d, IH, J = 7 Hz); 7.15 (bs, 4H); I3C NMR : 21.0, 21.1,40.5,40.8, 46.6, 87.5, 92.0, 95.9, 100.6, 110.3, 117.1, 127.5, 129.2, 129.4, 136.1 , 141.0, 199.5, 231.5. Anal. Calcd: C, 64.52; H, 4.33. Found: C, 64.96; H, 4.71 %.

Complex 11b: The reaction of alcohol 7b (100 mg, 0.25 mmole) with KH (10 mg, Immo)e) at O°C af­forded the complex ketone 11 b (81 mg, 81 %) as a red oil. IR : 1980, 1920,1690 cm-' ; 'H NMR : 2.35 (s, 6H); 2.45 (m, 2H); 3.10 (d, 2H, J = 7Hz); 3.40 (m, 1H); 5.05 (m, 4H); 5.55-5.85 (m, 3H); 7.15 (bs, 4H); I3C NMR : not recorded. Anal. Calcd: C, 64.52; H,4 .33. Found: C, 64.41 ; H, 4.89%.

Complex 12a: The reaction of alcohol 8a ( LOO mg, 0.25 mmole) with KH (10 mg, Immole) at O°C af­forded the ketone 12a (81 mg, 81 %) as a red oi I. IR : 1980, 1920, 1690 cm-' ;'H NMR : l.30 (m, 6H), 2.30 (s, 3H), 2.45 (t, 2H), 3.05 (m, 3H), 3.40 (m, 1 H), 5.00 (m, 2H), 5.15 (m, 2H), 5.30 (t, IH, J = 6Hz), 5.50 (d,

1070 INDIAN J. CHEM., SEC. B, NOVEMBER 2001

IH, J = 7Hz), 5.75 (m, IH), 7.10 (bs, 4H);l3C NMR : not recorded. Anal. Calcd: C, 66.00; H, 5.03. Found: C, 66.45; H,5.31 %.

Complex 12b: The reaction of alcohol8b (100 mg, 0.25 mmole) with KH (10 mg, Immole) at O°C af­forded the complex ketone 12b (81 mg, 81 %) as a red oil. IR : 1980, 1920, 1690 cm-';'H NMR : 1.30 (d, 3H), 1.45 (d, 3H) 2.30 (s, 3H), 2.40 (t, 2H), 3.05 (m, 3H), 3.40 (m, IH), 5.00 (m, 2H), 5.15 (m, 2H), 5.40-5.70 (m, 3H), 7.10 (bs, 4H);l3C NMR : not recorded. Anal. Calcd: C, 66.00; H, 5.03. Found: C, 66.228; H, 5.38%.

General procedure for the reaction of allyltri­methylsilane with complexes (1-4)

Dichloromethane (2 mL) was added to the complex (1-4, 0.5 mmole) and solution was cooled to -78°C. After 10 minutes, TiCI4 (1 mmole) was added drop­wise. The reaction mixture was stirred at this tem­perature for 30 minutes. Allyltrimethylsilane (0.4 mL, 2.5 mmole) in dichloromethane (1 mL) was added at the same temperature. The reaction was maintained at -50°C for 6-8 hr. The progress of the reaction was monitored by TLC. Once the reaction was over, the reaction mixture was cooled to -78°C and methanol (3 mL) was added dropwise. The reaction mixture was then allowed to warm to room temperature and then poured into degassed distilled water (15 mL) and ex­tracted with dichloromethane (20 mL). The crude product was subjected to column chromatography (15% ethyl acetate-pet. ether) to afford the desired products.

Complex 9a-b : The reaction of 1 (194 mg, 0.5 mmole) with allyltrimethylsilane (0.4 mL, 2.5 mmole) in presence of TiCl4 (190 mg, 1 mmole) afforded the mixture of complexes 9a-b (4:1, 182 mg, 85%) as orange-red solid. IR: 1980,1920, 1680 cm-';'H NMR : Signals corresponding to the major isomer - 2.33 (s, 3H); 2.40-2.55 (m, 2H); 3.15-3.55 (m, 3H); 3.88 (s, 3H); 4.80-5.15 (m, 5H); 5.60-5.90 (m, 2H); 6.15 (d, IH, J = 6Hz); 7.15 (m, 4H). Some signals corre­sponding to the minor isomer - 2.35 (s, 3H); 3.83 (s, 3H); 6.25 (d, IH, J = 6Hz); l3C NMR : Signals corre­sponding to the major isomer - 20.7, 40.3, 48.6, 55 .7, 72.1, 83.7, 90.8, 95.6, 116.2, 127.2, 128.9, 135.5, 136.4, 140.8, 143.8, 196.1,230.9. Some signals corre­sponding to the minor isomer - 40.1, 48.9, 72.4, 84.0, 95.1,116.3, 127.4, 136.1, 141.3, 196.2,231.1. Anal. Calcd: C, 64.30; H, 5.10. Found: C, 64.75; H,4.46%.

Complex lOb: The reaction of complex 2 (215 mg, 0.5 mmole) with allyltrimethylsilane (0.4 mL, 2.5

mmole) in presence of TiCl4 (190 mg, 1 mmole) af­forded the complex lOb (160 mg, 68%) as a red oil.

Complex lla-b : The reaction of 3 (186 mg, 0.5 mmole) with allyltrimethylsilane (0.4 mL, 2.5 mmole) in presence of TiCl4 (190 mg, 1 mmole) afforded the mixture of complexes lla-b (182 mg, 86%) as red solid in the ratio 1 :2. Chromatography yielded the pure complexes.

Complex 12a-b: The reaction of 4 (200 mg, 0.5 mmole) with allyltrimethylsilane (0.4 mL, 2.5 mmole) in presence of TiCl4 (190 mg, 1 rrunole) afforded the mixture of complexes 12a-b (179 mg, 81 %) as red solid in a ratio 1 :2.4. Chromatography yielded the pure complexes.

Procedure for allyl Grignard addition in pres­ence of TiC4.To a chilled solution of the complex 2 (315 mg, 0.73 mmole) pretreated with TiCl4 (0.3 mL) in dichloromethane (10 mL) at -90°C, aUylmagne­sium bromide (l mL of 1 M solution) was added dropwise with stirring. After 15 min the reaction was quenched with methanol and the product was isolated by flash chromatography as a coloured band. The 'H NMR spectrum of the product was identical with that of complex lOb.

Acknowledgement S.S. and S.K.M. thank the Council of Scientific and

Industrial Research, New Delhi, India and S.G. thanks the University Grants Commission, New Delhi , India, for research fellowships. The authors thank Mr B. C. Maity for generous assistance during preparation of the manuscript.

References 1 Sur S, Ganesh S, Pal D, Puranik V G, Chakrabarti P &

Sarkar, A, J Org Chem, 61, 1996, 8362. 2 For earlier results using this substrates. see: (a) Ganesh S &

Sarkar, A Tetrahedron Lett 32, 1991, 1085. (b) Ganesh S, Sathe K M, Nandi M, Chakrabarti P & Sarkar A, J Chem Soc Chem Commun, 1993,224. (c) Sur S, Ganesh S, Puranik V G & Sarkar A, J Chem Soc, Perkin Trans-I, 1998, 977.

3 For reviews on Hosomi-Sakurai Reaction: (a) Hosomi A, Acc Chem Res, 21,1988, 200. (b) Panek J S, In Camp Org Synthesis, Vol I, edited by Trost B M & Fleming 1 (Per­gamon Oxford),1991, 579. (c) Yamamoto Y & Sasaki N, Stereochemistry of Organometallic and Inorganic Com­pounds, vol 3, 363, edited by Bernal I, (Elsevier, Amste r­dam), 1989.

4 MandaI S K & Sarkar A, J Org Chem, 64, 1999, 2454. 5 Swamy V M, MandaI S K & Sarkar A, Tetrahedron Leu, 40,

1999,6061. 6 Uemura M, Oda H, Minami T & Hayashi Y, Tetrahedron

Lett, 32, 1991,4565. (b) Uemura M, Oda H, Minami T, Shi­roo M & Hayashi Y, Organometallics, II , 1992,3705.

SUR et 01.: HOSOMI -SAKURAI REACTION ON METAL-COMPLEXED ACYCLIC ENONES 1071

7 For discussions. see footnote 6 in ref I. and . Sur S, Ph D Thesis, University of Pune, 1997.

8 Although BFrOEt2 is also known to catalyze Hosomi­Sakurai reaction. and a transoid reactive geometry imposes no steric restriction on Lewi s ac id coordination to the ketone carbonyl function (as in Structure III. Chart 1), the substrate 2 fa iled to afford a product in presence of BFr OEt2 - the starting material was recovered unchanged afte r several hours. On the other hand , allylt rimethyl silane readily added to a-substituted benzaldehyde-Cr(COh complexes in pres­ence o f BFr OEt2 (S Sur. unpublished results) Taken to­gether, these observations indicated that a transition state for I A-addition cou ld not be attained by a possibl e in-pl ane co­ordination o f Lewis acid to the enone carbonyl held in tran ­soid geometry . Therefore, this poss ibility has not been con­sidered hereafter.

9 Reviews on anionic Oxy-Cope rearrangement: (a) Wilson S R, Anion Assisted Sigmatropic Rearrangements In Org Re­act. 43, 93 (b) Hill R K, Cope, Oxy-Cope and anionic oxy­Cope rearrangements In Camp Org Syn thesis. Vol 5, 785. ed ited by Trost B M & Fleming I, (Pergamon, Oxford), 199 1.

10 Deta il s o f crysta l structure determ ination will be publi shed separately. Crystals were grown from a mi xture of C H2CI2 and pet ether, data were collec ted on an Enraf-Nonius CAD-

4 single cry stal X- ray diffractometer using Mo Ka radi ation O. = 0 .70930 A). The structure was solved by direc t methods using NRCV AX program and refined (or being refined) by Full-matrix least-squares o n F2 using SHELXL-97. (a) The complex Sa, CD Hn OsCr. M = 430. crystal li zed in mono­clinic space group P2I/n , a = 7 .5240(18) b= 37.708(6), c = 8.0056(20) A, ~ = 111.83(2)A, V = 2 1 08.4(8)P, Z = 4 , Dc = 1.3 18 mg m-) Out of 4252 re flecti ons collected. only 2945

were in the 1>2.50(1)). and at present RI = 0.086, Rw = 0. 103. hydrogens are yet to be located. (b) The complex 9a. C2)H220 ,Cr. M = 430, Triclinic. space group P- I, a = 8.036(5) b = 10.053(2), c = 14.439(4) A, alpha =105.75 (2),~ = 80.38(3). gamma = 103.86(3) V = 1083.5(8) A1. Z = 2, D c = 1.3 19 Mg m-' Out of 3438 re fl ec ti ons collected. onl y 3 179

were in the 1>20(1)) , so fa r converged to RI = 0.0477, Rw = 0.1 408, hydrogens are to be located. (c) Compound 6b, C I6 HI S Cr OISi h Triclinic, space group P-I , a = 9.835(5) b = 10.894(2). c = 9.282(4) A, alpha =1 05 .75(2) , ~ = 95.04 ( I), gamma = 66.76(3) V = 1083 .5(8) A3. Z = 2 Yet to be re­fined .

II For an X-ray crystal structure of an analogous eno ne see ref 6b Also see: A Solladie-Cavallo in Advances in Metal­Organic Chemistry, vol I , pp 117- 11 8, edited by Liebeskind L S, (JAI Press), 1989.

12 (a) Reetz M T . Kesseler K, Schmidtberger S, Wenderoth B & Steinbach R, Angew Chern Int Ed (Engl), 22, 1983,989. (b) Reetz M T , Kesseler K & lung A, Angew Chern Int Ed (Engl), 24. 1985, 989. (c) Reetz M T & Jung A, J Am Chelll Soc, 105, 1983,4833. (d) Reetz M T, Kesse ler K & lung A, Tetrahedron Letl 1984, 25, 729.

13 Davies S G & McCarthy T D, Transition metal arene com­plexes: Side chain ac tivation and control of stereochemistry In Camp Organomet Chern II, vol 12, 1039, Abel E W, Stone F G A, edited by Wilkinson G. (Pergamon, Oxford), 1995 and references therein .

14 Davies earlier postulated a weak Si-O affinity to explain syn preference in a structurally related molecule: Davies S G & Goodfellow C L, J Chern Soc Perkin Trans-I, 1990,393.

15 (a) For a review on Lewis Acid-Carbonyl complexat ion, see: Shambayati S & Schre iber S L in Camp Org Synthesis" vol I p 283. edited by Trost B M & Fleming I (Pergamon, Ox­ford), 199 1. (b) Detailed spectroscopic studies on Lewis ac id-carbony l complex have been carried out by Denmark in order to probe stereoselec tivity in Lewis ac id promoted re­actions See : Denmark S E & Almstead N G, J Am Chem Soc. 11 5, 1993, 3 133 Also see: Denmark S E & Almstead N G, Tetrahedroll , 48, 1992,5565, and references 12 and 13 cited therei n. Leading references can be fou nd in : Klein D P & Gladysz J A, J Am Chelll Soc, 11 4. 1992, 8710 and refer­ences 4-6 in thi s paper, and , Harman W D, Fairl ie D P & Taube H, J Am Chem Soc. 108, 1986, 8223. For other refer­ences where Lewi s acids dictate the stereochemical outcome of a reac ti on, see: c) Fernandez J M. Emerson K, Larsen R H & Gladysz J A, J Am Chem Soc, 108. 1986, 8268. d) Klein D P & Gladyzs J A, J Am Chem Soc. 11 4 . 1992, 87 10. e) Springer 1 B & Corcoran R C, J Org Chem, 61, 1996, 1443. f) S ingh D K, Springer J B, Goodson P A & Corcoran R C, J Org Chefl/ . 61, 1996, 1436.

16 It was possible, however, to separate the isomeric products from Grignard reaction by fl ash column chromatography and independently rearrange them to si ngle product isomers.

17 In addition to refs 2b, 4 and 5, see: a) Fretzen A, Ripa A, Liu R, Bernardinelli G & Kundi g E P, Chem Eur J 4, 1998, 251 . b) Pigge F C, Fang S & Rath N P, J Orgallomel Chem. 559, 1998, 131.