4
Tetrahedron LettersNo. 32, pp. 2755-2758,1970. PergamonPress. Printed in Great Britain. THERMOLYSIS OF SPIR0[4.4]NONADIENE-I,3AND SPIRO[4.5]DECADIENE-I,3 *L.M.Da&, J.W. de Haan and **H.Kloosterziel. *Laboratory for Instrumental Analysis **Laboratory for Organic Chemistry University of Technology, Eindhoven, The Netherlands. (Received in UK 19 March 1970; acceptedfor publication 10 June 1970) As part of a study on the possible occurrence of thermal, suprafaeial, si@atropic 1,5 shifts of alkyl groups in geminally substituted cyclopentadienes (1,2) we re- port here the title reactions. Spirob.4) nonadiene-I,3 (?_a), diluted with nitrogen, is converted at 280'~ - 380'~ (residence times 30-140 set) by first-order kinetics to one major (*90%, by GLC) product 2_",an isomer (by massspectrum). Spectral (UV:x _= 255.5 nm, e = 2740 in isooctane; IR: characteristic absorption6 of cyclopentadiene and cyclohexene rings; NMR:s = 6.22-6.12 pp.8 = 2.76 ppm,s= 2.3-2.1 ppm,8 = 1.7-1.5 ppm, relative areas 2:2:4:4) and chemical (H2, Pt02 yielda trans- and cishexahydroindane) evidence pro- ve* that 2,"is 1,2-cyclopenta-11,31-dienocyolohexene. SpiroG.5) decadiene-I,3 (121, diluted with nitrogen, is converted at 380-445' (re- sidence times 40-180 set) by first-order kinetics to one major ( 90% by GLC) pro- duct 22, an isomer (by massspectrum). Spectral (HV:Xma= 246 nm, E = 3050 in iso- octane; IR: characterietia absorptione of cyclopentadiene and cgcloheptene rings; NMR:8= 5.90,8= 2.77,8= 2.42, a= 1.65, relative areas 2:2:4:6) evidence ehowlr that 2b ia 1,2-cyclopenta-l',31-dienecycloheptene. The data yielded the activation parameter6 given inthe Table. Table. Reaction "log A Ea(kcal/mol) &H$kcal/mol) l S#(oal/mol.degr) &G#(kcal/mol) la 2a 13.32 35.6 34.6 -1 35.0 lb 2b 15.09 46.7 45.5 +6 41.8

Thermolysis of spiro[4.4]nonadiene-1,3 and spiro[4.5]decadiene-1,3

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Tetrahedron Letters No. 32, pp. 2755-2758, 1970. Pergamon Press. Printed in Great Britain.

THERMOLYSIS OF SPIR0[4.4]NONADIENE-I,3 AND SPIRO[4.5]DECADIENE-I,3

*L.M.Da&, J.W. de Haan and **H.Kloosterziel.

*Laboratory for Instrumental Analysis

**Laboratory for Organic Chemistry

University of Technology, Eindhoven, The Netherlands.

(Received in UK 19 March 1970; accepted for publication 10 June 1970)

As part of a study on the possible occurrence of thermal, suprafaeial, si@atropic

1,5 shifts of alkyl groups in geminally substituted cyclopentadienes (1,2) we re-

port here the title reactions.

Spirob.4) nonadiene-I,3 (?_a), diluted with nitrogen, is converted at 280'~ - 380'~

(residence times 30-140 set) by first-order kinetics to one major (*90%, by GLC)

product 2_", an isomer (by massspectrum). Spectral (UV:x _= 255.5 nm, e = 2740 in

isooctane; IR: characteristic absorption6 of cyclopentadiene and cyclohexene rings;

NMR:s = 6.22-6.12 pp.8 = 2.76 ppm,s= 2.3-2.1 ppm,8 = 1.7-1.5 ppm, relative areas

2:2:4:4) and chemical (H2, Pt02 yielda trans- and cishexahydroindane) evidence pro-

ve* that 2," is 1,2-cyclopenta-11,31-dienocyolohexene.

SpiroG.5) d ecadiene-I,3 (121, diluted with nitrogen, is converted at 380-445' (re-

sidence times 40-180 set) by first-order kinetics to one major ( 90% by GLC) pro-

duct 22, an isomer (by massspectrum). Spectral (HV:Xma= 246 nm, E = 3050 in iso-

octane; IR: characterietia absorptione of cyclopentadiene and cgcloheptene rings;

NMR:8= 5.90,8= 2.77,8= 2.42, a= 1.65, relative areas 2:2:4:6) evidence ehowlr

that 2b ia 1,2-cyclopenta-l',31-dienecycloheptene.

The data yielded the activation parameter6 given inthe Table.

Table.

Reaction "log A Ea(kcal/mol) &H$kcal/mol) l S#(oal/mol.degr) &G#(kcal/mol) la 2a 13.32 35.6 34.6 -1 35.0

lb 2b 15.09 46.7 45.5 +6 41.8

2756 No. 32

Since I,5 shift6 of hydrogen in cyolopbntadibnb (Z-Dg are relatively fast (31, the

observed rates and the crucial question on the mbchadam of the ieombrieation of 1

pertain

Path A:

to tie convereion of Lint0 3. Two poesible proobssbs are to be coneidbrbd:

r.tno~mi+eq process involving ring opening to a biradicali followed by a

rfng ~SWurb.

Path B: a one-6tbp eigmatropia rbaation giving directly ring expansion.

a: n=4

b: I-l= 5

In the proceding letter it was oonoladed that thbrmolyai6 of apiro 2. heptadlenb-I,3 CJ

(1 with n=2) involves both path6 A and 8 with, aooidentally, comparable ratbe (in

# thi6 aase, n=2, path A doee not lead to 2). The data on the energy of activation, &H ,

and the rate (erpreseed as A5 # at 600'K) for J_ with n=2 will 6ervb a6 a basis to

616~~16 the pre6ent result6.

We assdllb that the tran6ition state for path A involve6 a total releaeb of the ring

strain 666OOiat6d with the (i1+1) ring of I_ and that the tran6ltion state for path B

involve6 one half of the difference between the ring strain of the (n+l) ring of 1

md that of the (n+2) ring of 3.

Path A for spire k.4 heptadiene-4,6 ha6 the valnes &= 45.8 andAQfkoo= 44.2 kcal/mol.

we asmme that the relative ring atrains (4) of ewith n=2, 4 and 5 are given by the

difference+ between the ring strain of oyclopropane (= 27.6) and those of oyclopentanb

(~6.5) and cyclohexane (= o koal/molb). Then the calculated value6 for 1," are:

~2, 45.8 + 27.6 - 6.5 = 67 # and a0 6W= 65 koal/mol. Similarly for I): rHf= 73 and

No. 32 2757

aG$OO= 72 kcal/mol. The values thus arrived at differ by about 30 kcal/mol with the

experimental data (Table).

Path B for epiroE.4 heptadiene-4,6 has the values AH f_ - 36.8 and&G $,,= 46.2

kcal/mol. We assume that the relative differences between the ring strains of L

and 3 are given by the ring strain of the appropriate (n+l) and (n+2)-cycloalkanes

(4). Then the calculated values for la are AH% 36.8 + 3 (146.5 - 145.4 + 140.8 -

146.9)=34 en aG'= 44 kcal/mol.

Similarly for 12: AHf= 41 and AG#= 30 kcal/mol.

The values thus arrived at differ by 1 to 8 (average 4) kcal/mol with the experi-

mental data. In view of the crudeness of the assumptions, we conclude that thermo-

lysis of 12 and 1-b involves suprafacial, sigmatropic !,.5 shifts of an alkylgroup

(3). The stereochemistry of these reactions is currently under investigation (6).

No. 32

REFERENCES :

(I) J.W. de Eaan and H.Moosteroiel, Rec.Trav.Chim. 3, 298 (1968).

(2) J.M,E,Erekels, J.W. de Raan and H.ICloosterziel, Tetrahedron Letters 1970,

(preceding paper).

(3) W.R.Roth, Tetrahedron Letters =, 1009.

(4) E.L.Eliel, Stereochemistry of Carbon Compounds, MacGraw-Hill, New York (1962).

(5) Thermochemical data (4) indicate that the similar reaction of Lwith n = 3 should

be relatively fast (calculated aIf+= 28 kcal/mole). Though the formation of

2 (n = 3) from cyclopentadiene and I,&-dibromopropane in the presence of a base

has been reported (71, we and others (8) have failed to obtain I_ (n = 3) in this

manner.

(6) After completion of this work the thermal conversion of ll to 2," was reported

without kinetic data (9).

(7) G.Chiurdoglu and B.l!ursch, Bull.Soc.Chim.Belges 66, 600 (1957).

(8) C.F.Wilcox and G.C.Whitney, J.Org.Chem. z, 2933, 3348 (1967).

(9) V.A.Mironov, A.P.Ivanov, Ya.M.ICimelfeld, L.I.Petrovskaya and A.A.Akhrem,

Tetrahedron Letters w, 3347.