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Photodecarbonylation: A novel photoreaction of rigid β,γ-enones
Tetrahedron Letters, Vol. 36, No. 19, pp. 3421-3424, 1995 Elsevier Science Ltd Printed in Great Britain 0040-4039/95 $9.50+0.00
Pergamon 0040-4039(95)00497-1
Photodecarbonylation : A Novel Photoreaction of Rigid 13,~-enones Vishwakarma Smgh , Beena Thomas and Uday Sharma Department of Chemistry, Indian Institute of Technology, Powai, Bombay -400 076. INDIA.
Abstract: A novel, photodecarbonylation upon singlet excitation of l~,7-enones having wider synthetic potential is described.
Photochemical reactions of 13,~/-unsaturated carbonyl chromophore has stimulated a great deal of interest in the pastl, 2 which is further enhanced due to their synthetic potential.2, 3 Though 13,yenones may undergo a variety of photoreactions characteristic of alkene and carbonyl chromophore,1 the 1,3-acyl shift and 1,2-acyl shift or oxa-di-rt-methane rearrangement are the two most commonly observed photoreactions of cyclic 13,7-enones, upon singlet(ls) and triplet excitations(3T)j respectively: In context with our exploratory studies on photoreaction of 13,~'enones, we recently observed a novel and efficient decarbonylation upon direct irradiation of 3-5 leading to tricyclic systems 6-8, and wish to record our results herein. It may be mentioned that this photoreaction offers a facile, potential route to carbocyclic framework of marasmanes, a class of biologically active sesquiterpenes, which have attracted interest recently. 4 The requisite chromophoric systems 3-5 were synthesized from a readily available common precursor 1. The reduction of 1 with zinc in protic solvent (CH3OH-H20) containing ammonium chloride furnished the ketoalcohol 2 (syn:anti mixture, 300 MHz, 1H NMR) as a major product which upon oxidation with Jones reagent followed by decarboxylation of the resulting I~-keto acid gave the parent system 5. Reduetive deoxygenation of epoxy ketone 1 with zinc in dry dioxane containing ammonium chloride yielded the monomethyl ketone 3a (syn:anti mixture, 300MHZ, 1H NMR) as a major product. Alkylation of 3a with methyl iodide and allyl bromide in presence of sodium hydride-THF gave chromophoric systems 3b 5 and 3e, respectively in good yields. Furthermore, the compound 3b was converted to diendione 45 via two fold oxidation with SeO 2 and Jones reagent (Scheme-I). Irradiation of a solution of 3b in benzene with a 400W mercury vapour lamp (Applied Photophysics) in a pyrex immersion well (2.5h), followed by removal of the solvent and careful chromotography of the pbotolysate furnished the tricyclic compound 6b in good yield (54%). The structure of the photoproduct was deduced from the spectral data.5 While the IR spectrum of 6b
3421
3422
i
1
iii
MOe•R2
~0
iv
C
a R 1 : Me, R2 : H (76%) b R 1= R2 : Me (34%) ~ c R 1= allyl, R2= Me (72%) vii
4 (45%)
ii
vii
R 1 R2 O
MeO 6a (52°1o), b (54%) c (35%)
2
MeO 7 (35%)
vi H vii
5 (30%)
>
H-
MeO 8
Scheme 1 Reagents and conditions: i, Zn, NH4Cl, dioxane ,A; ii, Nail, THF, Mel; iii, Nail, THF, allyl bromide; iv, SeO2, Jones reagent; v, Zn, NH4CI, MeOH - H20, r.t.; vi, Jones reagent, A ; vii, tw, pyrex (400 W, Hg vapour lamp), benzene/petroleum ether (40-60 ° )
did not show any absorption band due to carbonyl group, the presence of a cyclopropane ring was clearly evident from its 1H NMR (300MHz) which showed signals at 6 1.1 (dd, Jl = 9HZ, J2 : 6Hz, IH) and 0.64 (d, J = 9Hz, IH) for the protons at cyclopropane ring junctions. 6
Other
characteristic resonances were observed at 8 5.74 (m, 1H), 5.70 (m, 1H) and 4.71 (d with fine structure, J = 6Hz, IH) for olefinic protons in the five membered ring and vinyl ether moiety respectively. The signal for methoxy group was shown at 8 3.50 (s, 3H) and two methyls on the cyclopropane ring were observed at 8 1.07 and 0.85 as singlets in addition to other methine and methylene protons. 13C NMR of 6b also showed signals at 8 155.91 (s), 90.48 (d), 132.05 (d) and 129.54 (d) for the olefinic carbons of vinyl ether moiety and cyclopentene ring 7 Resonances at 54.00 (q), 41.89 (t), 28.11 (q), and 15.03 (q) corresponding to carbon atoms o f methoxy group, allylic methylene and methyl groups were also observed in addition to other signals.
3423
Encouraged by the above observation, we also irradiated other chromophoric systems 3a, 3c and 4 under above conditions which gave the corresponding decarbonylated products 6a, 6¢ and 7, respectively (Scheme.I) whose structures were clearly revealed through spectral data. 5 In this context, the decarbonylation of the highly functionalised system 4 having additional enone chromophore is noteworthy. Furthermore, the irradiation of the parent system 5 in petroleum ether (b.p.40-60°C) at ~I0°C also gave the decarbonylated product 8. Though the volatility of 2 hampered its isolation and determination of yield, it was easily characterized through 1H NMR. The detailed mechanism of formation of the decarbonylated products during the above photoreaction is difficult to suggest at this moment. Apparently it proceeds through initial ctcleavage 1 leading to 1,3-acyl shift product which subsequently undergoes decarbonylation to give the final product. This contention is based on the preliminary observation that 1,3-acyl shift product is formed during initial stages of the photoreaction which disappears after continued irradiation and the formation of final product is observed (tic). However the possibility of decarbonylation after initial ~t-cleavage can not be ruled out. In this context it may be noted that, such type of photodecarbonylation is generally not observedl, 8 during singlet excitation of constrained 13,)'-enones, though other reactions such as ketene formation and fragmentation are known. 9 In summary, we have reported a novel photodecarbonylation of 13,)'-enones having good synthetic potential and adaptability for the syntheses of marasmanes and their analogues. Strategic application of this photoreaction is underway. We thank R.S.I,C Bombay for providing high field 1H and 13C NMR spectra and Mr. K. Neurgaonkar for mass spectra, B. T. and U ,Sare grateful to C S . I R . for research fellowship. Financial support to V. S. from B R N . S . is gratefully acknowledged.
REFERENCES
1, Schuster, D. I. in Rearrangements in Ground and Excited States, P. de Mayo (ed), Academic Press, New York, 1980, vol 3, pp. 232-279; Houk, K. N , Chem. Rev., 1976, 76, 1-74 and references cited therein; Hixon, S. S., Mariano, P. S. and Zimmerman, H. E., Chem. Rev., 1973, 73, 531-551. 2. Demuth, M. in Organic Photochemistry, Padwa, A. (Ed.), Marcel Dekker Inc., New York, 1991, vol 11; pp 37-97; Singh, V. K., Deota, P. T. and Bedekar, A. V., J. Chem. Soc., Perkin I, 1992, 903-912. 3. Singh, V. K. and Thomas, B., J. Chem. Soc., Chem. Commun., 1992, 1211-1213. 4, Ayer, W~ A. and Browne, L. M., Tetrahedron, 1981, :$7, 2199-2248; Thompson, S. K. and Heathcock, C, H., J. Org. Chem., 1992, 57, 5979-5989; Boeekman, R. K, Jr. and Ko, S. S., J. Am. Chem. Soc., 1980, 102, 7146-7149; Greenlee, W. Land Woodward, R. B., J. Am. Chem. Soc., 1976, 98, 6075-6076; Hanson, T., Sterner, O. and Wickberg, B., J. Org. Chem., 1992, 57, 3822-3828.
3424
5, Selected data for 3b : IR Vmax (neat) : 1730 cm -1 ; UV ~,max (MeOH) : 216, 299 nm, 1H NMR (300 MHz, CDCI3) : 8 6.28 (dd, J1 = 9Hz, J2 = 7Hz, IH, y-H of [3,y-enone moiety), 6.20 (d with long range coupling, J = 9Hz, 1H, I~H of 13,y-enone moiety), 5.72 (complex m, IH, olefinie H), 5.60 (complex m, 1H, olefinic H), 3.55 (s, 3H, OCH3) , 3.17 (complex m of d, J = -10Hz, 1H, methine H), 3.00 (m, 1H, methine H), 2.62 (m, 1H, methine H), 2.53 (m ofdd, J1 = 18Hz, J2 = 10.8Hz, 1H, methylene H), 1.97 (m of d, J = 18Hz, 1H, methylene H), 1.12 (s, 3H, CH3) , 1.05 (s, 3H, CH3); 13C NMR (75MHz, CDCI3) : 6 214.74 (CO), 134.09, 133.90, 128.70, 128.23 (olefinic carbons), 87.27, 53.6, 51.90, 48.08, 44.1, 39.29, 36.68, 27.65 and 23.95; Mass (m/z) : 218 (M+). 4 : mp, 121-122°C; IR Vmax (nujol) : 1730, 1700 era-l; 1H NMR (300 MHz, CDCi3) : 6 7.57 (dd, J1 = 6Hz, J2 = -2Hz, IH, 13 H ofc~,l~-enone moiety), 6.33 (dd, J1 = 6Hz, J2 = 1.SHz, 1H, 0t H of ct,l~-enone moiety), 6.23 (dd, J1 = 9Hz, J2 = 7Hz, 1H, y H of [3,y-enone moiety), 5.9 (d, J = 9Hz, 1H, 13 H of J3,y-enone moiety), 3.6 (s, 3H, OCH3) , 3.36 (m of d, J = 6Hz, 1H, methine H), 3.03 (complex m, 1H, methine H), 2.90 (dd, J1 = 6Hz, J2 = 3Hz, 1H, methine H), 1.21 (s, 3H, CH3), 1.19 (s, 3H, CH3); 13C NMR (75MHz, CDCI3) : 8 212.46, 208.7 (two CO's), 161.38, 137.86, 132.99, 125.51 (olefinic carbons), 86.73, 53.58, 45.80, 45.33, 44.21, 42.64, 26.92, 23.23; Mass (m/z) : 232 (M+). 6b: IR Vmax (neat) : 3050, 3000, 2950 and 1650 cm'l; 1H NMR (300 MHz, CDCI3) : 6 5.74 (m, IH) , 5.68 (m, 1H), 4.71 (d with structure, J = 6 Hz, 1H, H C = C-OMe), 3.5 (s, 3H, OCH3), 2.88 (br d, J = 8Hz, IH, methine H), 2.72 (m, 1H, ring junction H), 2.68 (m of ddd, J = 12Hz, 1H, allylic methylene), 2.3 (m o f d d d , J = 12 Hz, 1 H, allylic methylene), 1.1 (dd, J1 = 9Hz, J 2 = 6Hz, 1H, cyclopropyl ring junction H), 1.07 (s, 3H, CH3), 0.85 (s, 3H, CH3) , and 0.64 (d, J = 9Hz, 1H, cyclopropane ring junction H). 13C NMR (75MHz~ CDCI3) : 8 155.91, 132.05, 129.54, 90.48, 54,00, 46.69, 41.89, 34.23, 28.11, 26.19, 22.92, 22.54 and 15.03; Mass (m/z) : 190 (M+). 7 : IR Vmax (neat) • 1705, 1670 c m ' l ; 1H NMR (300 MHz, CDCI3) fi " 7157 (dd, J1 = 6Hz, J2 = 3Hz, 1H, [3 H, of ct,13-enone group), 6.16 (dd, J1 = 6Hz, J2 .= -3Hz, 1H, ct-H of tx,l~-enone group), 4.77 (dd, J1 = 5Hz, J2 = -2 Hz, IH, vinyl proton of enol ether moiety), 3.58 (s, 3H, OCH3), 3.24 (br d with structure, J = 8 Hz, 1H allylic ring junction H), 2.72 (d, J = 8Hz, 1H, proton at ring junction ct' to carbonyl), 1.14 (muitiplets merged with a singlet, total 5H, CH 3 and eyclopropane ring junction protons ) and 0.9 (s, 3H, CH3); 13C NMR (75MHz, CDCI3) : 8 211.21 (CO), 164.58, 152.13, 131.80, 91.92 ( olefinic carbons), 54.26, 44.10, 42.94, 27.22, 22.57, 21.99, 20.84 and 15.04 ; Mass (m/z) : 204 (M +) 6. Jackman, L. M. and Sternhell, S. in Application of NMR Spectroscopy in Organic Chemistry, Pergamon Press, New York, 1969; Marchand, A. P. in Stereochemical Applications of NMR Studies in Bicyclic Systems, Verlag Chemic International, FI., 1982. 7. Levy, G. C. and Nelson, G. L. in Carbon-13 Nuclear Magnetic Resonance for Organic Chemists, Wiley Interscience, New York, 1977, vol. 2. 8. Seharf, H. D. and Kusters, W., Chem. Ber., 1971, 104, 3016-3029. 9. Parker, S. D. and Rogers, N. A. J., Tetrahedron, 1984, 40, 3749-3758.
(Received in UK 28 February 1995; accepted 17 March 1995)
Pergamon 0040-4039(95)00497-1
Photodecarbonylation : A Novel Photoreaction of Rigid 13,~-enones Vishwakarma Smgh , Beena Thomas and Uday Sharma Department of Chemistry, Indian Institute of Technology, Powai, Bombay -400 076. INDIA.
Abstract: A novel, photodecarbonylation upon singlet excitation of l~,7-enones having wider synthetic potential is described.
Photochemical reactions of 13,~/-unsaturated carbonyl chromophore has stimulated a great deal of interest in the pastl, 2 which is further enhanced due to their synthetic potential.2, 3 Though 13,yenones may undergo a variety of photoreactions characteristic of alkene and carbonyl chromophore,1 the 1,3-acyl shift and 1,2-acyl shift or oxa-di-rt-methane rearrangement are the two most commonly observed photoreactions of cyclic 13,7-enones, upon singlet(ls) and triplet excitations(3T)j respectively: In context with our exploratory studies on photoreaction of 13,~'enones, we recently observed a novel and efficient decarbonylation upon direct irradiation of 3-5 leading to tricyclic systems 6-8, and wish to record our results herein. It may be mentioned that this photoreaction offers a facile, potential route to carbocyclic framework of marasmanes, a class of biologically active sesquiterpenes, which have attracted interest recently. 4 The requisite chromophoric systems 3-5 were synthesized from a readily available common precursor 1. The reduction of 1 with zinc in protic solvent (CH3OH-H20) containing ammonium chloride furnished the ketoalcohol 2 (syn:anti mixture, 300 MHz, 1H NMR) as a major product which upon oxidation with Jones reagent followed by decarboxylation of the resulting I~-keto acid gave the parent system 5. Reduetive deoxygenation of epoxy ketone 1 with zinc in dry dioxane containing ammonium chloride yielded the monomethyl ketone 3a (syn:anti mixture, 300MHZ, 1H NMR) as a major product. Alkylation of 3a with methyl iodide and allyl bromide in presence of sodium hydride-THF gave chromophoric systems 3b 5 and 3e, respectively in good yields. Furthermore, the compound 3b was converted to diendione 45 via two fold oxidation with SeO 2 and Jones reagent (Scheme-I). Irradiation of a solution of 3b in benzene with a 400W mercury vapour lamp (Applied Photophysics) in a pyrex immersion well (2.5h), followed by removal of the solvent and careful chromotography of the pbotolysate furnished the tricyclic compound 6b in good yield (54%). The structure of the photoproduct was deduced from the spectral data.5 While the IR spectrum of 6b
3421
3422
i
1
iii
MOe•R2
~0
iv
C
a R 1 : Me, R2 : H (76%) b R 1= R2 : Me (34%) ~ c R 1= allyl, R2= Me (72%) vii
4 (45%)
ii
vii
R 1 R2 O
MeO 6a (52°1o), b (54%) c (35%)
2
MeO 7 (35%)
vi H vii
5 (30%)
>
H-
MeO 8
Scheme 1 Reagents and conditions: i, Zn, NH4Cl, dioxane ,A; ii, Nail, THF, Mel; iii, Nail, THF, allyl bromide; iv, SeO2, Jones reagent; v, Zn, NH4CI, MeOH - H20, r.t.; vi, Jones reagent, A ; vii, tw, pyrex (400 W, Hg vapour lamp), benzene/petroleum ether (40-60 ° )
did not show any absorption band due to carbonyl group, the presence of a cyclopropane ring was clearly evident from its 1H NMR (300MHz) which showed signals at 6 1.1 (dd, Jl = 9HZ, J2 : 6Hz, IH) and 0.64 (d, J = 9Hz, IH) for the protons at cyclopropane ring junctions. 6
Other
characteristic resonances were observed at 8 5.74 (m, 1H), 5.70 (m, 1H) and 4.71 (d with fine structure, J = 6Hz, IH) for olefinic protons in the five membered ring and vinyl ether moiety respectively. The signal for methoxy group was shown at 8 3.50 (s, 3H) and two methyls on the cyclopropane ring were observed at 8 1.07 and 0.85 as singlets in addition to other methine and methylene protons. 13C NMR of 6b also showed signals at 8 155.91 (s), 90.48 (d), 132.05 (d) and 129.54 (d) for the olefinic carbons of vinyl ether moiety and cyclopentene ring 7 Resonances at 54.00 (q), 41.89 (t), 28.11 (q), and 15.03 (q) corresponding to carbon atoms o f methoxy group, allylic methylene and methyl groups were also observed in addition to other signals.
3423
Encouraged by the above observation, we also irradiated other chromophoric systems 3a, 3c and 4 under above conditions which gave the corresponding decarbonylated products 6a, 6¢ and 7, respectively (Scheme.I) whose structures were clearly revealed through spectral data. 5 In this context, the decarbonylation of the highly functionalised system 4 having additional enone chromophore is noteworthy. Furthermore, the irradiation of the parent system 5 in petroleum ether (b.p.40-60°C) at ~I0°C also gave the decarbonylated product 8. Though the volatility of 2 hampered its isolation and determination of yield, it was easily characterized through 1H NMR. The detailed mechanism of formation of the decarbonylated products during the above photoreaction is difficult to suggest at this moment. Apparently it proceeds through initial ctcleavage 1 leading to 1,3-acyl shift product which subsequently undergoes decarbonylation to give the final product. This contention is based on the preliminary observation that 1,3-acyl shift product is formed during initial stages of the photoreaction which disappears after continued irradiation and the formation of final product is observed (tic). However the possibility of decarbonylation after initial ~t-cleavage can not be ruled out. In this context it may be noted that, such type of photodecarbonylation is generally not observedl, 8 during singlet excitation of constrained 13,)'-enones, though other reactions such as ketene formation and fragmentation are known. 9 In summary, we have reported a novel photodecarbonylation of 13,)'-enones having good synthetic potential and adaptability for the syntheses of marasmanes and their analogues. Strategic application of this photoreaction is underway. We thank R.S.I,C Bombay for providing high field 1H and 13C NMR spectra and Mr. K. Neurgaonkar for mass spectra, B. T. and U ,Sare grateful to C S . I R . for research fellowship. Financial support to V. S. from B R N . S . is gratefully acknowledged.
REFERENCES
1, Schuster, D. I. in Rearrangements in Ground and Excited States, P. de Mayo (ed), Academic Press, New York, 1980, vol 3, pp. 232-279; Houk, K. N , Chem. Rev., 1976, 76, 1-74 and references cited therein; Hixon, S. S., Mariano, P. S. and Zimmerman, H. E., Chem. Rev., 1973, 73, 531-551. 2. Demuth, M. in Organic Photochemistry, Padwa, A. (Ed.), Marcel Dekker Inc., New York, 1991, vol 11; pp 37-97; Singh, V. K., Deota, P. T. and Bedekar, A. V., J. Chem. Soc., Perkin I, 1992, 903-912. 3. Singh, V. K. and Thomas, B., J. Chem. Soc., Chem. Commun., 1992, 1211-1213. 4, Ayer, W~ A. and Browne, L. M., Tetrahedron, 1981, :$7, 2199-2248; Thompson, S. K. and Heathcock, C, H., J. Org. Chem., 1992, 57, 5979-5989; Boeekman, R. K, Jr. and Ko, S. S., J. Am. Chem. Soc., 1980, 102, 7146-7149; Greenlee, W. Land Woodward, R. B., J. Am. Chem. Soc., 1976, 98, 6075-6076; Hanson, T., Sterner, O. and Wickberg, B., J. Org. Chem., 1992, 57, 3822-3828.
3424
5, Selected data for 3b : IR Vmax (neat) : 1730 cm -1 ; UV ~,max (MeOH) : 216, 299 nm, 1H NMR (300 MHz, CDCI3) : 8 6.28 (dd, J1 = 9Hz, J2 = 7Hz, IH, y-H of [3,y-enone moiety), 6.20 (d with long range coupling, J = 9Hz, 1H, I~H of 13,y-enone moiety), 5.72 (complex m, IH, olefinie H), 5.60 (complex m, 1H, olefinic H), 3.55 (s, 3H, OCH3) , 3.17 (complex m of d, J = -10Hz, 1H, methine H), 3.00 (m, 1H, methine H), 2.62 (m, 1H, methine H), 2.53 (m ofdd, J1 = 18Hz, J2 = 10.8Hz, 1H, methylene H), 1.97 (m of d, J = 18Hz, 1H, methylene H), 1.12 (s, 3H, CH3) , 1.05 (s, 3H, CH3); 13C NMR (75MHz, CDCI3) : 6 214.74 (CO), 134.09, 133.90, 128.70, 128.23 (olefinic carbons), 87.27, 53.6, 51.90, 48.08, 44.1, 39.29, 36.68, 27.65 and 23.95; Mass (m/z) : 218 (M+). 4 : mp, 121-122°C; IR Vmax (nujol) : 1730, 1700 era-l; 1H NMR (300 MHz, CDCi3) : 6 7.57 (dd, J1 = 6Hz, J2 = -2Hz, IH, 13 H ofc~,l~-enone moiety), 6.33 (dd, J1 = 6Hz, J2 = 1.SHz, 1H, 0t H of ct,l~-enone moiety), 6.23 (dd, J1 = 9Hz, J2 = 7Hz, 1H, y H of [3,y-enone moiety), 5.9 (d, J = 9Hz, 1H, 13 H of J3,y-enone moiety), 3.6 (s, 3H, OCH3) , 3.36 (m of d, J = 6Hz, 1H, methine H), 3.03 (complex m, 1H, methine H), 2.90 (dd, J1 = 6Hz, J2 = 3Hz, 1H, methine H), 1.21 (s, 3H, CH3), 1.19 (s, 3H, CH3); 13C NMR (75MHz, CDCI3) : 8 212.46, 208.7 (two CO's), 161.38, 137.86, 132.99, 125.51 (olefinic carbons), 86.73, 53.58, 45.80, 45.33, 44.21, 42.64, 26.92, 23.23; Mass (m/z) : 232 (M+). 6b: IR Vmax (neat) : 3050, 3000, 2950 and 1650 cm'l; 1H NMR (300 MHz, CDCI3) : 6 5.74 (m, IH) , 5.68 (m, 1H), 4.71 (d with structure, J = 6 Hz, 1H, H C = C-OMe), 3.5 (s, 3H, OCH3), 2.88 (br d, J = 8Hz, IH, methine H), 2.72 (m, 1H, ring junction H), 2.68 (m of ddd, J = 12Hz, 1H, allylic methylene), 2.3 (m o f d d d , J = 12 Hz, 1 H, allylic methylene), 1.1 (dd, J1 = 9Hz, J 2 = 6Hz, 1H, cyclopropyl ring junction H), 1.07 (s, 3H, CH3), 0.85 (s, 3H, CH3) , and 0.64 (d, J = 9Hz, 1H, cyclopropane ring junction H). 13C NMR (75MHz~ CDCI3) : 8 155.91, 132.05, 129.54, 90.48, 54,00, 46.69, 41.89, 34.23, 28.11, 26.19, 22.92, 22.54 and 15.03; Mass (m/z) : 190 (M+). 7 : IR Vmax (neat) • 1705, 1670 c m ' l ; 1H NMR (300 MHz, CDCI3) fi " 7157 (dd, J1 = 6Hz, J2 = 3Hz, 1H, [3 H, of ct,13-enone group), 6.16 (dd, J1 = 6Hz, J2 .= -3Hz, 1H, ct-H of tx,l~-enone group), 4.77 (dd, J1 = 5Hz, J2 = -2 Hz, IH, vinyl proton of enol ether moiety), 3.58 (s, 3H, OCH3), 3.24 (br d with structure, J = 8 Hz, 1H allylic ring junction H), 2.72 (d, J = 8Hz, 1H, proton at ring junction ct' to carbonyl), 1.14 (muitiplets merged with a singlet, total 5H, CH 3 and eyclopropane ring junction protons ) and 0.9 (s, 3H, CH3); 13C NMR (75MHz, CDCI3) : 8 211.21 (CO), 164.58, 152.13, 131.80, 91.92 ( olefinic carbons), 54.26, 44.10, 42.94, 27.22, 22.57, 21.99, 20.84 and 15.04 ; Mass (m/z) : 204 (M +) 6. Jackman, L. M. and Sternhell, S. in Application of NMR Spectroscopy in Organic Chemistry, Pergamon Press, New York, 1969; Marchand, A. P. in Stereochemical Applications of NMR Studies in Bicyclic Systems, Verlag Chemic International, FI., 1982. 7. Levy, G. C. and Nelson, G. L. in Carbon-13 Nuclear Magnetic Resonance for Organic Chemists, Wiley Interscience, New York, 1977, vol. 2. 8. Seharf, H. D. and Kusters, W., Chem. Ber., 1971, 104, 3016-3029. 9. Parker, S. D. and Rogers, N. A. J., Tetrahedron, 1984, 40, 3749-3758.
(Received in UK 28 February 1995; accepted 17 March 1995)