J. CHEM. soc. PERKIN TRANS. I 1994 Synthesis Based on Cyclohexadienes. Part 15.' Total Synthesis of ( ? )-Prezizaene, ( k )-Prezizanol and ( k )-Jinkohol II Natesan Selvakumar and G. S. R. Subba Rao" Department of Organic Chemistry, Indian Institute of Science, Bangalore-5600 12, India A new methodology for the synthesis of the complex ring system tricycl0[6.2.1.0'~~] undecane, present in the zizaene group of sesquiterpenes, is described. Acid-catalysed rearrangement of the endo alcohol 20 afforded the enone 12, which was transformed stereoselectively into the key intermediate, ( +)-norprezizanone 10. The features of the synthesis are the transformation of a bicyclo[2.2.2]octane framework into a bicyclo[3.2.1 ]octane system by an acid-catalysed rearrangement and a stereoselective conjugate addition of a methyl group on an a,p-unsaturated keto ester at -100"C.Norprezizanone was converted into the sesquiterpenes ( +)-prezizanol 5 and ( k )-prezizaene 4. The first total synthesis of ( +)-jinkohol I1 6 is also presented. A large number of natural tricyclic sesquiterpenes possess the tricyclo[6.2.1 .0'*5]undecane skeleton. These include zizaene 1,2 khusimol 2,3 and zizanoic acid 3,, which were isolated from vetiver oil of various regions, prezizaene 4,5prezizanol 5 and jinkohol I1 6,6isolated from vetiver oil and japanese agarwood. It is interesting to note that these unusual tricyclic sesqui- terpenes have been found only in vetiver oil and agarwood oil and possess a strong woody note. Two distinct biogenetic schemes have been postulated to rationalize the unusual ring system, substitution pattern and stereochemistry of zizaene and its congener^.'.^ Total synthesis of these sesquiterpenes is a challenge to synthetic chemists, since they possess (i) a novel tricy-cloc6.2.1 .0'.5]undecane skeleton, (ii) four one-carbon substitu- ents at C-7 (geminal dimethyl), C-6 and C-2, (iii) a spiro-fused ring system and (iv) a thermodynamically less stable trans-fused ethanohydrindane nucleus.Owing to their unique molecular structure, interesting biogenesis and their importance as perfumery products, several syntheses of zizaene and its congeneric relatives have been reported. We have earlier reported" the preparation of the tricyclic compounds 8 and 9 required for the synthesis of cedrene and 1 R=Mezizaene 4 R'R2 = CH2 prezizaene 2 R = CH20Hkhusimol 5 R' = Me, R2= OH prezizanol 3 R = C02Hzizanoic acid 6 R' = H, R2 = CH20Hjinkohol II Results and Discussion We have chosen norprezizanone 10 as the key intermediate of our synthesis and this can be made from the tricyclic enone 12 through the sequence of reactions outlined in Scheme 1.C02Me BnO I \-- -0 10 11 J-& J@ a 0 0 12 13 Scheme 1 Preparation of the Intermediate 13.-The starting material for the preparation of the tricyclic enone 12 is the readily available 6-methoxytetralin 14 which was converted into enone 12 as shown in Scheme 2. Birch reduction of compound 14 yielded the dihydro compound 15, which was subjected to a (4+ 2) cycloaddition with a-chloroacrylonitrile in refluxing benzene for 48 h to afford a mixture of adducts 16 and 17 in 97% yield. Hydrolysis' of the mixture of adducts 16 and 17 with aq.KOH in dimethyl sulfoxide (DMSO) at 60 "C for 45 h gave the known tricyclic ketone 18.', Compound 18 on reduction with NaBH, afforded a 2 :1 mixture of the endo and the exo alcohols 20 and 19 respectively. However, reduction of the ketone 18 with diisobutylaluminium hydride (DIBALH) yielded a 19:1 mixture of endo and exo alcohols, which was separated by HoBd omMeO column chromatography. The alcohols were characterized on 7 6 9 zizaene, by an acid-catalysed rearrangement of the alcohols 7. Although the compound 9 could be converted' 'into zizaene by appropriate transformations, only an epimeric mixture (C-2) of zizaene was obtained, We now describe an efficient stereo- controlled total synthesis of (& )-prezizaene 4, ( *)-prezizanol5 and ( k )-jinkohol I1 6.A preliminary account of this work has been reported. l2 the basis of their 'H NMR spectra, wherein the C-9 proton appeared as a doublet of a doublets due to a W-coupling in the spectrum of exo-compound 19, while the endo-alcohol 20 displayed a broad doublet for the same proton. The endo- alcohol 20, upon treatment with BF,*Et,O in refluxing benzene for 20 h, rearranged to the enone 12 in 94% yield. Under identical conditions the exo-alcohol 19 afforded the isomeric ketone 21. The structures of the compounds 12 and 21 were deduced from their spectral data; in particular, the IR spectrum of compound 12 showed the presence of ,x,P-unsaturated 3218 J.CHEM. SOC. PERKIN TRANS. 1 1994 14 =15 16 RICI, R~= CN 17 R' = CN,R2 = CI 20 12 19 21 Scheme 2 Reagents: (a), Na, liq. NH,; (b), CH,=C(CI)CN, PhH, reflux; (c) KOH, DMSO; (d) DIBALH; (e) BF,.OEt,; (f) NaOH, furfural(2-furaldehyde) carbonyl absorptions at 1610 and 1680 cm-' while that of compound 21 showed an absorption band at 1722 cm-' due to the saturated ketone. In addition the 'H and 13CNMR spectra of the ketones 12 and 21 were consistent with the proposed structure. Furthermore, compound 21 gave a crystalline furfurylidene derivative, 22, the structure of which was confirmed by X-ray crystallography. The mechanism of the formation of the ketones 12 and 21 from the endo and exo alcohols 20 and 19 can be visualized by the concerted migration of the antiperiplanar C-C bonds with respect to the OH group.Synthesis of Tricyclic Ketone 33.-Alkylation ' of the enone 12 with KOBu' and Me1 in refluxing benzene furnished the ketone 23 in 75% yield (Scheme 3). Reduction of ketone 23 with NaBH, gave the alcohol, which was converted into its benzyl ether 24 on treatment with sodium hydride and benzyl bromide in excellent yield. Hydroboration of the cyclohexene 24 followed by oxidative work-up resulted in the expected secondary alcohol, which was oxidized with pyridinium chlorochromate (PCC) to the ketone 13in high yield.The stereochemistry of the hydrogen at the ring junction was assumed to be a, since the addition of BH, is expected to take place from the less hindered a side of the molecule, as the p side is crowded by an axial ethano bridge and an axial methyl group. The tricyclic ketone 13was converted l6 into the dicarboxylic ester 26 by ozonolysis of its furfurylidene derivative 25 followed by oxidative work-up and esterification of the resultant diacid. Dieckmann con-densation of the diester 26 with KOBu' in refluxing benzene afforded the P-keto ester 11. The 'H NMR spectrum of compound 11 showed distinct singlets for the two methyl groups and a doublet for the C-7 proton, indicating it to be a single diastereoisomer. Having achieved the basic tricycloC6.2.1 .0'~5]undecane framework, our next task was to introduce an a-methyl group at the C-2 position stereoselectively.This could in principle be achieved by a conjugate addition of Me,CuLi on the unsaturated ketone 29, since it was expected that the methyl group would approach from the less hindered a-face of the molecule. Decarboxylation of the keto ester 11with NaC1-DMSO l7 at 150 "C afforded the ketone 27 in 88% yield (Scheme 4). Treatment of 27 with lithium diisopropylamide (LDA) and PhSeCl' * followed by oxidative elimination of the intermediate selenide with aq. H,O, resulted in an inseparable mixture (4: 1) 23 24 Ic Bno-enoJ&0 0 25 13le BnOp::Me fBnoRCO&le 26 11 Scheme 3 Reagents and conditions: (a) KOBu', MeI, PhH, reflux (75%); (b) (i) NaBH,, EtOH, room temp., 2 h; (ii) NaH, PhCH,Br, Bu,NI, THF, 0 "C to room temp., 24 h (98%);(c) (i) BH,-THF, THF, 0 "C to room temp., 5 h, then aq.NaOH, 30% H,O,; (ii) PCC, CH,CI,, 1 h (77%); (d) NaOH, furfural, EtOH, 0 "C to room temp., 7 h; (e) (i) 0,,EtOAc, -78 "C, then 30% H,O,, AcOH, 24 h; (ii) CH,N,, Et,O, 0 "C (70%); (f) KOBu', PhH, reflux, 17 h (78%) bl II J = 3.1k J = 6.9 HZ i'63.19 63.46 29 30 31 9 BnO BnO&P 32 33 Scheme4 Reagentsandconditions:(a) NaCI, DMSO, 150 "C; (b) LDA, PhSeCI, H,O,; (c) NaOMe; (d) Me,CuLi; (e) NaH, PhSeCI, H,O,; (f) Me,CuLi, -100 "C; (g) DABCO, o-xylene of enones 29 and 30, as evidenced by the 'H NMR spectrum, indicating that epimerization of the C-5 proton had taken place.When the spectrum of the above mixture was recorded after the sample had been kept in CDCl, for 24 h, we observed a rapid conversion of the trans-enone 29 into the cis compound 30from an initial (4 :1) ratio into a (1 :1) mixture. The signal for the C-7 proton in the 'H NMR spectrum was diagnostic for estimating the ratio of this mixture. In the trans compound the C-7 proton J. CHEM. SOC. PERKIN TRANS. 1 1994 appeared at 6 3.19 (J 3.1 Hz), while it appeared at 6 3.46 (J 6.9 Hz) for the cis compound. The peak positions were assigned for these epimers on the basis of the observed coupling constants. Examination of molecular models indicated that the 6-membered ring in the irans compound assumes a chair conformation, while in the cis compound it exists in a boat conformation.The dihedral angle of the proton on C-7 with C-8 changes from 60" for the trans compound to 40" for the cis compound and hence there is an increase in the coupling constant. This (1 :1) mixture on being left in the NMR tube in CDCl, became a (1 :4) mixture after 6 days. Furthermore, with a catalytic amount of NaOMe in refluxing methanol this mixture was completely converted into the cis compound 30. Owing to this unexpected isomerization at the ring junction, the enone 29 was subjected to a 1,4-addition reaction im- mediately after its preparation. Thus, reaction of compound 27 with LDA, PhSeCl and H,O, resulted in an oil, which was allowed to react with Me,CuLi l9 at OOC, to give the ketone 32, whose H NMR spectrum showed a pair of doublets for the C-2 methyl group, indicating the absence of selectivity during the 1,4-addition reaction.Owing to the poor selectivity during the addition of Me,CuLi on the enone 29 at 0 "C, we anticipated that the addition might take place stereoselectively at low temperature on the enone ester 28. Treatment of the keto ester 11 with NaH and PhSeCl gave the selenide, which was oxidized with H,02 to yield the unstable enone ester 28. Reaction of compound 28 with Me,CuLi in dry diethyl ether at -100 "C, afforded the P-keto ester 31 in 88% yield as an unstable oil. The P-keto ester 31 was found to be a mixture of two diastereoisomers from its 'H NMR spectrum, as it displayed two peaks for the methoxycarbonyl group, presumably due to epimers at the centre bearing the methoxycarbonyl group.This was confirmed by decarboxylation of the mixture of P-keto esters to give a single isomer of ketone 33, whose 'H NMR spectrum showed a lone doublet for the C-2 methyl group, indicating that a stereoselective conjugate addition of methyl group had taken place. It is of interest to note that the NaCI- DMSO decarboxylation procedure on the keto ester 31 failed to give good yields of the product 33, although decarboxylation of the keto ester 11 afforded the ketone 27 in 88% yield. In search for a mild procedure for the decarboxylation of keto ester 31, 1,4-diazabicyclo[2.2.2] octane (DABCO) in o-xylene 2o at 85 "C proved to be superior giving the ketone 33 in 84% yield.Synthesis of ( k)-Norprezizanone 10.-Having achieved the stereoselective 1,4-addition, our next task was the reduction of compound 33 to ketone 10. Attempted Wolff-Kishner reduc- tion resulted in an epimeric mixture of the tricyclic compound 34, wherein the C-5 proton isomerized under the reaction conditions (Scheme 5). Even the modified Wolff-Kishner reduction21 with the mild base K,CO, also led to iso-merization. This problem could be circumvented by the use of Barton's deoxygenation protocol 22 on the alcohol 35, obtained from the ketone 33. Reduction of the ketone 33 with NaBH,, LiAIH, and BH, resulted in partial reduction to the alcohol 35. However, with excess of DIBALH, the ketone 33 was reduced to the alcohol 35 in 93% yield.The xanthate 36 was obtained by treatment of the alcohol 35 with excess of NaH and successive quenches with CS, and MeI. Reduction of the xanthate 36 with tributyltin hydride (TBTH) in refluxing benzene resulted in only the recovery of the starting material. In refluxing toluene, a partial elimination of the xanthate was observed after 12 h. However, when the reduction was carried out by successive addition of TBTH twice with an interval of 3 h, the benzyl ether 37 was obtained in excellent yield. The ether 37, thus obtained as a single isomer, was hydrogenolysed to the alcohol 38, which was oxidized with pyridinium dichromate (PDC) to afford (+)-34 35 R=OH 36 R=OC!&Me 37 R=H f HO 5 38 0.--.i HOCH2HP@ 4 6 Scheme 5 Reagents and conditions: (a) Wolff-Kishner reaction; (b) DIBALH, THF, -78 "C to room temp. (93%); (c) NaH, CS,, MeI, THF, reflux (98%);(d) TBTH, AIBN, PhMe, reflux (91%);(e) H,, 10% Pd/C, EtOH, 2 h (100%);(f) PDC, CH,CI,, 2 h (100%);(8) MeLi, Et,O, -78 "C to room temp. (88%); (h) MsCl, Et,N, CH,CI,, 0 OC (76%); (i) Wittig reaction (78%); (j) BH,.THF, THF, 0 OC then 30% H,O, (72%) norprezizanone 10 in quantitative yield. The IR and 'H NMR spectra of compound 10 were identical with those of an authentic sample provided by Professor Kenji Mori. The synthesis of prezizaene and prezizanol has been reported by three different groups9d,e*h and all of them involve norprezizanone 10 as the common intermediate.In all the syntheses either a mixture of products was formed which required HPLC separation or a large number of steps were involved to obtain norprezizanone. Our synthesis of nor-prezizanone was accomplished in 13 steps from 6-methoxy- tetralin 14, with an overall yield of 10.6%. Synthesis of Sesquiterpenes 4, 5 and 6.-Mori and co-workers 9h have converted norprezizanone 10 into prezizanol and prezizaene. By application of the same sequence of reactions, compound 10 afforded ( k)-prezizanol5 with MeLi. Dehydration of alcohol 5 gave ( k)-prezizaene 4. Wittig olefination of compound 10 also directly yielded ( + )-prezizaene 4, which upon hydroboration followed by oxidation gave (+ )-jinkohol I1 6 in good yield.The spectral data of compound 6 were identical6 with those reported, thus completing the first total synthesis of this compound. Since prezizaene 4 has been converted into zizaene I, a formal total synthesis of zizaene has also been achieved. In conclusion, we describe a novel and efficient method of total synthesis of the sesquiterpenes prezizaene 4, prezizanol 5 and jinkohol I1 6, which contain the complex tricyclo- C6.2.1 .0'~5]undecane ring system, from readily available dihydroanisole derivatives. Experimental M.p.s (measured on Mettler FP1) and b.p.s are uncorrected. IR spectra were recorded on either neat samples or solutions in CHCl,. 'H NMR and 13C NMR spectra were recorded on solutions in CDCl, with SiMe, as internal standard.Chemical shifts are reported in &units, and J-values are in Hz. The usual work-up involved dilution of the reaction mixture with water, extraction with diethyl ether, washing of the organic extract with water and brine, followed by drying over Na,SO,, and evaporation at aspirator pressure. Column chromatography was performed on silica gel (60-120 mesh) by elution with a light petroleum (boiling range 60-80 "C)-ethyl acetate mixture (9: 1). Liquid ammonia was distilled over sodium amide. Sodium hydride was 60% in oil, and was used after washing with light petroleum. 9-Chloro-8-methoxytricyc10[6.2.2.0''6]dodec-6-ene-9-carbo-nitrile 16 and 17.-A solution of 6-methoxytetralin 14 (24.3 g, 0.15 mol) in dry tetrahydrofuran (THF) (1 5 cm3)-tert-butyl alcohol (30 cm3) was added to stirred, distilled ammonia (500 cm3).Sodium (6.9 g, 0.3 mol) was added and the resulting blue solution was stirred for 2.5 h. Solid NH4CI was added until the blue colour was discharged. NH, was allowed to evaporate, and the residue was worked up with light petroleum to give the diene 15as a liquid, vmax/cm-' 1670, 1450 and 1220. The diene 15, 2-chloroacrylonitrile (35.5 cm3,0.45 mol) and hydroquinone (10 mg) were refluxed in dry, stirred benzene (120 cm3) for 48 h. The reaction mixture was concentrated under reduced pressure and distilled at reduced pressure (b.p. 132- 135 "C at 0.1 mmHg) to give the adducts 16 and 17 as a viscous oil (36.6 g, 97%); v,,,/cm-' 2225; 6,(60 MHz) 1.30-2.40 (14 H, m), 3.52 (3 H, s, OMe) and 5.83 and 6.00 (1 H, two br s, olefinic) (Found: C, 66.7; H, 7.2.C14H18CIN0 requires C, 66.8; H, 7.2%). 8-Methoxytricycl0[6.2.2.0'~~]dodec-6-en-9-one18.-The ad-ducts 16 and 17 (25.1 g, 0.10 mol) and 20% aq. KOH (56 cm', 0.20mol) were stirred in DMSO (1 10 cm') at 60 "C for 40 h. The reaction mixture obtained after the usual work-up furnished by chromatography a yellow oil, which was distilled under reduced pressure to provide the tricyclic ketone 18as an oil, b.p. 105 "C (0.1 mmHg); v,,,/cm-' 1733; 6,(90 MHz) 1.50-2.40 (14 H, m), 3.52 (3 H, s, OMe) and 5.82 (1 H, br s, olefinic); &(50 MHz) J. CHEM. SOC. PERKIN TRANS. 1 1994 Evaporation of the solvent followed by purification by chromatography afforded the enone 12 as an oil (4.96 g, 94%), v,,,/cm-' 1680and 1610;6,(90 MHz) 1.4&2.50(14 H, m), 2.78- 2.9 (1 H, m, 9-H) and 5.66 (1 H, br s, olefinic); &(22.5 MHz) 22.58(t),24.27(t),26.74(t),30.64(t),34.54(t),35.19(t),45.34(t), 46.25 (s), 48.98 (d), 122.07 (d), 170.32 (s) and 202.71 (s) (Found: C, 81.7; H, 9.2%; M', 176.1210.C12H160 requires C, 81.8; H, 9.15%; M, 176.1201). Tricycl0[6.3.1 .01*6]dodec-5-en-9-one 21 .-When the exo-alcohol 19(312 mg, 1.5 mmol) in dry benzene was refluxed with BF3-Et,0 (cat.) as described above, the ketone 21 (227 mg, 86%) was obtained as an oil, vmax/cm-' 1722; &(90 MHz) 1.20- 2.80 (15 H, m) and 5.60 (1 H, br s, olefinic); 6,(22.5 MHz) 18.28 (t), 24.79 (t), 32.59 (t), 34.15 (t), 34.41 (t), 35.71 (t), 41.18 (s), 44.56 (t), 48.20 (d), 120.12 (d), 141.32 (s) and 212.72 (s) (Found: M', 176.1215).7,7-Dimethyltricyclo[7.2.1.0'*6Jdodec-5-en-8-one 23.-To a slurry of KOBu' in tert-butyl alcohol, prepared from potassium (2.93 g, 75 mmol) and dry tert-butyl alcohol (40 cm3), was added a solution of the enone 12 (4.40 g, 25 mmol) in dry benzene (1 00 cm3). After stirring of the mixture for 30 min, Me1 (15.6 an3, 0.25 mol) was added rapidly and the mixture was refluxed for 2 h before being brought to room temp. and a further quantity of Me1 (4 cm3) was added. The resulting solution was stirred for 6 h and the usual work-up followed by chromatographic purification afforded the ketone 23 (3.83 g, 7579, which crystallized upon refrigeration.An analytical sample was obtained by bulb-to-bulb distillation (1 25 "C, bath temperature; 0.1 mmHg), m.p. 47 "C; v,,,/cm-' 17 12 and 1672; 6,(90 MHz) 1.28(6H,s,Me),1.40-2.20(12H,m),2.86(1H,m,9-H)and5.52 (1 H, t, J4, olefinic);6,(22.5 MHz) 20.23 (q), 25.57 (t), 27.91 (t), 30.25 (t), 31.81 (q), 36.23 (t), 37.27 (t), 39.74(t), 44.17 (s), 46.51 (s), 50.54 (d), 119.21 (d), 148.99 (s) and 217.80 (s) (Found: C, 82.4; H, 10.0%; M+, 204.1529. C14H200 requires C, 82.3; H, 9.9%; M, 204.1514). 8-Benzyioxy-7,7-dimethyit ricy cio[7.2.1.0'p6]dodec-5-ene 24. 18.30,20.44,25.98,27.03,30.49,31.24,38.48,45.16,52.44,84.20,-To 119.39, 148.57 and 209.17 (Found: C, 75.3; H, 9.2%; M+, 206.1315. C13HlgO2 requires C, 75.7; H, 8.8%; M, 206.1307).endo-8-Methoxytricycl0[6.2.2.0',6Jdodec-6-en-9-01 20.-A 1.2 mol dm-' solution of DIBALH (45.8 cm', 55 mmol) in toluene was added to a solution of ketone 18(10.30 g, 50 mmol) in dry THF (160 cm') dropwise at -78 "C under argon. The mixture was stirred at -78 "C for 30 min, warmed to room temp. over a period of 15 min, and quenched with methanol (20 cm3). The resulting solution was treated with saturated aq. sodium potassium tartrate (500 cm3) to get a clear solution, which after the usual work-up showed two closely moving spots on TLC (&-values 0.35 and 0.30; 20% EtOAc in light petroleum). The mixture was chromatographed; the less polar component was the exo-alcohol 19 (469 mg), v,,,/cm-' 3440; 6,(90 MHz) 1.30-2.60 (15 H, m), 3.22 (3 H, s, OMe), 3.86 (1 H, dd, J 2.5 and 10.8, CHOH) and 5.40 (1 H, br s, olefinic).The more polar component was the endo-alcohol 20 (8.91 g, 90% overall yield, exo :endo ratio 5 :95); v,,,/cm-' 3440; 6,(90 MHz) 1.20-2.40 (15 H, m), 3.40 (3 H, s, OMe), 3.92 (1 H, d, J 9, CHOH) and 5.72 (1 H, br s, olefinic) (Found: C, 74.85; H, 9.6. C, ,H2,02 requires C, 75.0; H, 9.6%). Tricyclo[7.2.1 .0'*6]dodec-6-en-8-one 12.-A solution of endo- alcohol 20 (6.24 g, 30 mmol) in dry benzene (150 cm3) was heated under reflux with BF,.Et,O (1 cm') for 20 h. The reaction mixture was diluted with benzene (300 cm'), washed successively with aq. NaHCO,, water, and brine, and was dried. a solution of ketone 23 (3.06 g, 15 mmol) in ethanol (100 cm') was added NaBH, (284 mg, 7.5 mmol) at room temp.After being stirred for 2 h, the reaction mixture was concentrated under reduced pressure and was poured into aq. NH,CI (500 cm3). The usual work-up followed by chromato- graphy afforded the corresponding alcohol, vmax/cm-' 3355. A mixture of this alcohol and benzyl bromide (1.87 cm', 15.7 mmol) in dry THF (30 cm') was added to a suspension of NaH (660 mg, 16.5 mmol) and tetrabutylammonium iodide (cat.) in dry THF (90 cm') at 0 "C dropwise under argon. The reaction mixture was brought to room temp. during 1 h and was stirred for 24 h at ambient temperature. The usual work-up, followed by filtration through a column of silica gel, yielded the ether 24 as an oil (4.35 g, 98%). An analytical sample was obtained by bulb-to-bulb distillation (1 80 "C, bath temperature; 0.1 mmHg), v,,,/cm-' 1452,732 and 696; 6,(90 MHz) 1.14 (3 H, s, Me), 1.18 (3H,s, Me), 1.26-2.10(12H,m),2.44-2.64(1H,m,9-H), 3.18 (1 H, d, J3,8-H), 4.38 and4.72(2 H, AB,, J 12, OCH2Ph), 5.44 (1 H, t, J 4, olefinic) and 7.28-7.44 (5 H, m, Ph); 6,(22.5 MHz) 21.23 (t), 23.47 (q), 26.69 (t), 27.96 (q), 31.17 (d), 37.90 (t), 40.63 (s), 43.56 (t), 44.73 (s), 71.15 (t), 88.02 (d), 117.77 (d), 127.22 and 128.30 (2 d, 5 aromatic carbons), 139.80 (s) and 151.70 (s) (Found: C, 84.6; H, 9.4%; M+, 296.2130. C21H280 requires C, 85.1; H, 9.5%; M, 296.2140).8-Benzyioxy-7,7-dimethyltricyci0[7.2.1.O' *6]dodecan-5-one 13.-To a solution of compound 24 (3.55 g, 12 mmol) in dry THF (100 cm3) was added 1.2 mol dm-' BH3-THF (30 cm', 36 mmol) dropwise at 0 "C under argon.The resultant mixture was J. CHEM. soc. PERKIN TRANS. 1 1994 brought to room temp. during 1 h and was stirred for a further 5 h at ambient temperature before being carefully quenched with drops of water, and 20% aq. NaOH (3.6 an3,18 mmol) and 30% aq. H,02 (4.1 cm3, 36 mmol) were added with occasional cooling. After stirring of the mixture for 3 h, the usual work-up and chromatography afforded the C-5 alcohol (2.90 g, 7779, v,,,/cm-' 34 1 8. The alcohol (2.83 g, 9 mmol), PCC (2.44 g, 11.3 mmol) and silica gel (3 g) were stirred in dry CH2Cl, (60 cm3) at room temp. for 1 h. The solvent was removed, and the resultant powder was dissolved in diethyl ether and filtered through a pad of Celite.The filtrate was evaporated, and the residue was passed through a column of silica gel to give the ketone 13 as a viscous oil (2.81 g, loo%), which crystallized upon storage. An analytical sample was obtained by recrystallization in light petroleum, m.p. 72 "C; vmax/m-'1704; 6,(90 MHz) 1.18 (3 H, s, Me), 1.34(3H,s,Me), 1.52-2.56(14H,m), 3.04(1 H,d, J3,8-H), 4.42 and 4.70 (2 H, AB,, J 12, OCH,Ph) and 7.28-7.44 (5H, m, Ph); 6,(22.5 MHz) 16.08 (q), 22.84 (t), 24.79 (t), 31.68 (q), 32.59 (d), 37.53 (s), 38.57 (t), 43.00 (t), 46.51 (t), 48.46 (s), 64.71 (d), 71.22 (t), 88.25 (d), 127.01 and 128.18 (2 d, 5 aromatic carbons), 139.37(s)and 209.2 1(s)(Found: C, 80.5; H, 9.1%; M ,3 12.2087. + C2,H2,0, requires C, 80.7; H, 9.0%; M, 312.2090).Methyl 4-Benzyloxy-l-[2-(methoxycarbonyl)ethyl]-3,3-di-methylbicyclo[3.2.l]octane-2-carboxylate26.-T0 a solution of the ketone 13 (2.25 g, 7.2 mmol) in ethanol (60 cm3) at 0 "C under argon was added 20% aq. NaOH (1.44 cm3, 7.2 mmol) dropwise, and the resultant solution was stirred for 30 min. A solution of freshly distilled furfuraldehyde (0.6 cm3, 7.2 mmol) in ethanol (1 cm3) was added, and the reaction mixture was warmed to room temp. and stirred for 7 h. Usual work-up gave the condensation product 25 as a yellow solid which was used directly in the next step without purification. A solution of enone 25 in ethyl acetate (80 cm3) was ozonized at -78 "C until TLC indicated the disappearance of starting material.The solvent was removed at 10 "C under reduced pressure, and the resultant gum was treated with acetic acid (40 cm3), 30% aq. H,O, (10 cm3) and dil. H2S04 (1 cm3). The mixture was stirred overnight and concentrated at 40 "C under reduced pressure. The residue was dissolved in diethyl ether (400 cm3), and washed with brine, and the solvent was evaporated to give a solid. A solution of the above dicarboxylic acid in dry diethyl ether (200 cm3) was esterified with ethereal diazomethane. The solvent was evaporated off and the residue was purified on a column to obtain the diester 26 as a solid (1.96 g, 70%), which was recrystallized from ethyl acetate, m.p. 67 "C; v,,,/cm-' 1737; 6,(90 MHz) 1.08 (3 H, s, Me), 1.10 (3 H, s, Me), 1.20-2.60 (12H,m),3.14(1 H,d,J3,4-H),3.68(6H,s,C02Me),4.36and 4.68 (2 H, AB,, J 12,0CH2Ph) and 7.32 (5 H, br s, Ph); 6,(22.5 MHz) 19.06 (q), 24.01 (q), 29.86 (t), 30.51 (t), 33.1 1 (t), 33.37 (t), 37.79(t),41.57(t),45.73(~),50.54(q),51.19(q),58.99(d),71.22 (t), 86.82 (d), 127.01 and 127.92 (2 d, 5 aromaticcarbons), 138.98 (s), 172.53(s) and 173.70 (s) (Found: C, 71.1; H, 8.4.C23H3205 requires C, 71.1; H, 8.3%). Methyl 7 -Benzyloxy-6,6-dimethyl-4-oxotricyclo C6.2.1.0' * '1 -undecane-3-carboxylate 11.-To a freshly prepared solution of KOBu' in tert-butyl alcohol prepared from potassium (21 1 mg, 5.4 mmol) and dry tert-butyl alcohol (7 cm3), was added a solution of the diester 26 (1.75 g, 4.5 mmol) in dry benzene (80 cm3) at room temp. under argon.The solution was refluxed for 6 h and then was allowed to cool to room temp. The reaction mixture was added to aq. NH,C1 and extracted with ethyl acetate (4 x 200 cm3). The usual work-up followed by chromatography afforded the P-keto ester 11 as an unstable oil (1.25 g, 78%j, v,,,/cm-' 1755 and 1731;6,(200 MHz) 1.13 (3 H, 322I s, Me), 1.19 (3 H, s, Me), 1.25-2.55 (10 H, m),3.17 (1 H, d, J 3, 7-H), 3.26 (1 H, dd, J 8.3 and 11.7,3-H), 3.74 (3 H, s, CO,Me), 4.42 and 4.69 (2 H, AB,, J 12,OCH,Ph) and 7.28-7.35 (5H, m, Ph); 6,(67.89 MHz) 16.53 (q), 24.66 (t), 32.48 (q), 33.04 (t), 36.14 (t), 38.60 (s), 39.92 (d), 43.36 (t), 47.87 (s), 53.00 (q), 55.99 (d), 67.36 (d), 72.71 (t), 89.05 (d), 128.02 and 128.94 (2 d, 5 aromatic carbons), 139.97 (s), 170.85 (s) and 208.73 (s) (Found: M+, 356.1981.C22H2804requires M, 356.1988). 7-Benzyloxy-6,6-dimethyltricycloC6.2.1.0' * S]undecan-4-one 27.-A mixture of the P-keto ester 11 (356 mg, 1 mmol), NaCl (64 mg, 1.1 mmol), water (0.04 cm3) and DMSO (5 cm3) was heated to 150 "C for 8 h. The reaction mixture was cooled, and the usual work-up followed by chromatography yielded the ketone 27 (262 mg, 88%), v,,,/cm-' 1734; &(90 MHz) 1.18 (3 H, s, Me), 1.24(3 H, s, Me), 1.36-2.64(12H, m), 3.18 (1 H,d, J 3,7-H), 4.44 and 4.72 (2 H, AB,, J 12,OCH,Ph) and 7.36 (5 H, br s, Ph); 6,(100 MHz) 15.90, 23.91, 31.20, 31.26, 32.50, 37.69, 38.52,39.13,42.95,49.53,66.68,71.80,88.51,127.25 and 128.20 (5 aromatic carbons), 139.31 and 216.38 (Found: M', 298.1958. C,,H,,O, requires M, 298.1933).7-Benzyloxy-6,6-dimethyltricycloC6.2.1 .O 9 '1 undec-2-en-4-one 29 and M.-A 1.6 mol dm-3 solution of BuLi in hexane (0.63 cm', 1 mmol) was added to a solution of diisopropylamine (0.14 cm3, 1 mmol) in THF (1 cm3) at -78 "C under argon. After this mixture had been stirred for 30 min, a solution of the ketone 27 (268 mg, 0.9 mmol) in THF (2 cm3) was added dropwise. The resultant mixture was stirred for 1 h, and a solution of PhSeCl (192 mg, 1 mmol) in THF (1 cm3) was added at once. After being stirred for 15 min, the cold reaction mixture was poured into aq. NH4Cl and worked up to afford the corresponding seleno compound. To a mixture of the above crude seleno compound in CH,Cl, (4 cm3) was added 30% aq.H202 (0.26 cm3, 2.25 mmol) at 5 "C. After being stirred for 30 min, the reaction mixture was diluted with CH,Cl,, washed with water, and dried. The residue obtained after chromatography afforded the enones 29 and 30 (165 mg, 62x1, v,,,/cm-' 1713. Enone 29: 6&00 MHz) 1.19 (3 H, s, Me), 1.26 (3 H, s, Me), 1.34-2.52(8H,m),3.19(1 H,d, J3.1,7-H),4.44and4.70(2H, AB,, J 12, OCHZPh), 5.94 (1 H, d, J 5.7, 3-H), 7.28-7.36 (5 H, m, Ph) and 7.42 (1 H, d, J 5.7,2-H). Enone 30:6&00 MHzj 1.01 (3 H, s, Me), 1.32-2.60 (8 H, m), 1.39 (3 H, s, Me), 3.46 (1 H, d, J6.9, 7-H), 4.37 and 4.55 (2 H, AB,, J 12,OCH,Ph), 6.09 (1 H, d, J5.7, 3-H), 7.26-7.34 (5 H, m, Ph) and 7.51 (1 H, d, J 5.7, 2-H) (Found: M+, 296.1790. C20H2402requires M, 296.1776).Isomerization of trans-Enone 29 to cis-Enone 30.-To a mixture of enones 29 and 30 (27 mg, 0.1 mmol) in dry benzene (3 cm3) was added NaOMe (cat.) and the solution was refluxed for 4 h. The resultant mixture was cooled, poured into ice-cold 1 mol dm-, HC1, and worked up as usual. The enone 30 was obtained after filtration through a short column of silica gel (23 mg, 86%). 7-Benzyloxy-2,6,6-trirnethyltricyclo[6.2.1.O .5]undecan-4-one 33.-A solution of P-keto ester 11 (445 mg, 1.25 mmol) in dry THF (5 cm3) was added to a suspension of NaH (75 mg, 1.88 mmol) in dry THF (10 cm3j over a period of 10 min at 0 "C under argon. After the mixture had been stirred for 15 min, a solution of PhSeCl (264 mg, 1.38 mmol) in THF (5 cm3) was added rapidly, and the mixture was stirred for an additional 15 min.The cold reaction mixture was poured into an ice-cold mixture of diethyl ether (50 cm3) and saturated aq. NaHCO, (50cm3), and was worked up as usual to obtain the selenide as a pale orange solid. To a mixture of this crude selenide in CH,Cl, (10 cm3) was added 30% aq. H,O, (0.27 cm3, 2.4 mmol) dropwise at 5 "C. After being stirred at 5 "C for 10 min, the reaction mixture was warmed to room temp. over a period of 15 min. The resultant product mixture was diluted with CH,Cl,, washed with water, and dried. The residue was chromatographed to afford the unsaturated keto ester 28, which was immediately used in the next step (412 mg, 93%), v,,,/cm-' 1752 and 1725. To a suspension of CuI (221 mg, 1.16 mmol) in dry diethyl ether (10 cm3) at 0 "C under argon was added 0.87 mol dmP3 MeLi (2.65 cm3, 2.32 mmol) in diethyl ether.The resultant solution of Me,CuLi was stirred for 5 min and cooled to -100 "C. A solution of the unsaturated keto ester 28 (41 1 mg, 1.16mmol) in dry diethyl ether (10 cm3) was added slowly, and the reaction mixture, after being stirred for 30 min, was quenched with aq. NH,Cl. The usual work-up followed by chromatography furnished the P-keto ester 31 as an oil. (378 mg, 8879, vmax/cm-l 1755 and 1731; dH(200 MHz) 1.02 (3 H, d, J 7.3,2-Me),1.13,1.17, 1.18and1.23(6H,4s,Me),1.35-2.56(9 H, m), 2.96 (dd, J 2.1 and 1.4) and 3.42 (d, J 8.6) (together 1 H, 3-H), 3.10 (1 H, 2 dd, 2-H), 3.71 and 3.73 (3 H, 2 s, CO,Me), 4.55 (2 H, AB,, J 12,OCH,Ph) and 7.36 (5 H, m, Ph).A mixture of the P-keto ester 31 (370 mg, 1 mmol), DABCO (1.12 g, 10 mmol) and o-xylene (5 cm3) was heated to 85 "C under argon for 7 h. The reaction mixture was cooled, acidified with 0.5 mol dm HCI and worked up as usual. The ketone 33 was obtained as a crystalline solid after purification by chromatography (262 mg, 84%), and was recrystallized from light petroleum, m.p. 126 "C; vmaX/cmp'1740; 6&00 MHz) 1.04 (3 H, d, J7.2, 2-Me), 1.14 (3 H, s, Me), 1.21 (3 H, s, Me), 1.26- 2.55 (1 1 H, m), 3.1 1 (1 H, dd, J3.0 and 1.l, 7-H), 4.42and4.70 (2 H, AB,, J 12, OCH,Ph) and 7.29-7.37 (5 H, m, Ph); &(lo0 J. CHEM. SOC. PERKIN TRANS. 1 1994 cm3) was refluxed for 5 min under argon.To this refluxing solution was added dropwise a mixture of the xanthate 36(1 58 mg, 0.39 mmol) and azoisobutyronitrile (AIBN) (cat.) in toluene (2 cm3). Refluxing was continued for 6 h, and a further quantity of TBTH (0.21 cm3, 0.78 mmol) with AIBN (cat.) in toluene (1 cm3) was added. The resultant mixture was refluxed for an additional 5 h and all volatiles were then removed under reduced pressure. The residue obtained upon chromatography on neutral alumina and elution with light petroleum yielded the benzyl ether 37 (106 mg, 91%) as an oil, v,,,/cm-' 1455,732 and 696; 6&00 MHz) 0.87 (3 H, d, J 7.2, 2-Me), 0.97 (3 H, s, Me), 0.98 (3 H, s, Me), 1.061.98 (12 H, m), 2.02-2.49 (1 H, m, 8-H), 3.15 (1 H, dd, J3.0 and 1.1,7-H), 4.41 and 4.70 (2 H, AB,, J 12, OCH,Ph) and 7.25-7.40 (5 H, m, Ph); 6,-(22.5 MHz) 16.21 (q), 18.81 (q), 21.67 (t), 22.19 (t), 31.20 (q), 32.42 (t), 36.75 (s), 37.79 (t), 38.05 (d), 38.83 (d), 51.98 (s), 52.70 (d), 70.47 (t), 87.63 (d), 126.12 and 126.99 (2 d, 5 aromatic carbons) and 138.69 (s) (Found: M', 298.2300.C2,H3,0 requires M, 298.2296). 2,6,6-Trimethyltricyclo[6.2.1.0'.5]undecan-7-ol 38.-A solu-tion of the benzyl ether 37 (89 mg, 0.3 mmol) in absolute ethanol (6 cm3) was stirred with 10% Pd/C (10 mg) under H,. After 2 h the catalyst was filtered off on Celite and the filtrate was chromatographed to give the alcohol 38 (62 mg) in quantitative yield, v,,,/cm-' 3345; 6,(200 MHz) 0.81 (3 H, d, J 7.2, 2-Me), 0.85(3 H, s, Me), 0.94 (3 H, s, Me), 1.01-1.96 (1 3 H, m), 2.14 (1 H, m, 8-H) and 3.41 (1 H, dd, J 3.0 and 0.7, 7-H); 6,(100 MHz) 16.51,19.83,22.90,22.91,32.54,33.22,33.35,37.80,39.52,39.99, 44.69, 53.72, 53.80 and 81.20 (Found: M+, 208.1852.Calc. for CI6H2,O: M, 208.1827). 2,6,6-Trimethyltricyclo[6.2.1.0'*5]undecan-7-one 10.-A mix-MHz) 16.09,17.66,23.68,32.58,34.03,35.66,37.41,38.89,39.14,ture of alcohol 38 (52 mg, 0.25 mmol), PDC (188 mg, 0.5 46.57, 52.1 1, 60.95, 71.60, 88.19, 127.10 and 128.03 (5 aromatic carbons), 139.13 and 216.30 (Found: C, 80.7; H, 9.4%; M', 3 12.2090. C,,H,,O, requires C, 80.7; H, 9.0%, M, 3 12.2090). 7-Benzyloxy-2,6,6-trimethyltricyc1~[6.2.1.0'*5]undecane 37. -A 1 mol dm-3 solution of DIBALH in hexane (0.90 cm3, 0.90 mmol) was added to a mixture of ketone 33 (140 mg, 0.45 mmol) in dry THF (5 cm3) under argon at -78 "C.The mixture was stirred for 1 h and a further quantity of DIBALH (0.90 cm3, 0.90 mmol) was added. After being stirred for 1 h at -78 OC, the reaction mixture was left at room temp. for another 1 h before being quenched with MeOH (1 cm3) and poured into saturated aq. sodium potassium tartrate. The usual work-up and chromatography afforded the alcohol 35 (1 3 1 mg, 93% yield), v,,,/cm-' 3360; dH(9O MHz) 0.92 (3 H, d, J7.2, 2-Me), 1.10 (3 H, s, Me), 1.32 (3 H, s, Me), 1.36-2.60 (12 mmol) and silica gel (200 mg) in dry CH,Cl, (5 cm3) was stirred for 2 h. The solvent was completely removed to give a dark powder, which was taken in diethyl ether and filtered through a pad of Celite and silica gel.The filtrate was concentrated and the residue was chromatographed to obtain the ketone 10 (51 mg) in quantitative yield, vmax/cmp' 1700; 6,(400 MHz)0.91 (3 H, d, J7.2,2-Me), 1.068 (3 H, s, Me), 1.072 (3H,s,Me), 1.13-2.14(12H,m)and2.76(1 H,m,8-H);dC(100 MHz) 19.93,22.54,24.37,27.59,28.81,31.98,32.09,37.94,39.86, 45.70, 52.22, 53.72, 54.09 and 219.62 (Found: M+, 206.1697. Calc. for C14H22O: M, 206.1671). ( k )-Prezizanol5.-When the ketone 10 (33 mg, 0.16 mmol) was treated with 0.85 mol dmp3 MeLi (0.56 cm3, 0.48 mmol) as per the procedure of Mori,'" prezizanol 5 (31 mg, 88%) was obtained, v,,,/cm-' 3420; 6,(90 MHz) 0.87 (3 H, s, Me), 0.88 H,m),3.10(1 H,d,J3,7-H),4.32-4.78(3H,m,0CH2Phand(3 H, d, J7,2-Me), 1.01 (3 H, s, Me), 1.23 (3 H, s, Me) and 1.40- 4-H) and 7.22-7.44 (5 H, m, Ph); dC(22.5 MHz) 18.10 (q), 18.69 (q), 23.18 (t), 33.32 (q), 36.73 (t), 39.01 (d), 39.36 (d), 40.73 (s), 45.70 (t), 51.55 (s), 60.04 (d), 71.54 (t), 73.10 (d), 88.22 (d), 127.22 and 128.10 (2 d, 5 aromatic carbons) and 139.51(s).To a suspension of NaH (64 mg, 1.6 mmol) and imidazole (cat.) in dry THF (2 cm3) was added a solution of the alcohol 35 (126 mg, 0.4 mmol) in dry THF (2 cm3) under argon, and the mixture was refluxed for 2 h before being cooled, a solution of freshly distilled CS, (0.24 cm3, 4 mmol) in THF (1 cm3) was added, and this mixture was heated at reflux. After 45 min, the reaction mixture was cooled, a solution of Me1 (0.25 cm3, 4 mmol) in THF (1 cm3) was added, and the mixture was refluxed for 30 min.After the usual work-up, the residue was filtered through a column of silica gel with light petroleum as eluent to yield the xanthate 36 as a yellow oil (159 mg, 98%), vmax/cm-l 1450 and 1050. A solution of TBTH (0.21 cm3, 0.78 mmol) in dry toluene (5 2.10 (13 H, m) (Found: M', 222.1983. Calc. for C15H2,0: M, 222.1984). ( k )-Prezizaene 4.-According to Mori,'" when prezizanol5 (22 mg, 0.1 mmol) in dry CH,Cl, (3 cm3) was treated with Et,N (0.5cm3) and MeSO,Cl(O.3 cm3), prezizaene 4 was obtained as an oily liquid (1 5 mg, 76%), vmax/cm-' 3070, 1625 and 890; 6,(90 MHz) 0.87 (3 H, d, J7,2-Me), 1.07 (3 H, s, Me), 1.10 (3 H, s, Me), 1.15-2.08 (12 H, m), 2.81 (1 H, t, 8-H) and 4.65 and 4.71 (2 H, AB,, J 1.8, olefinic) (Found: M+,204.1855.Calc. for Cl5H2,O: M, 204.1878). ( k )-Jinkohol I1 6.-To a solution of K'OAm [prepared from potassium (1 2 mg, 0.3 mmol) and dry tert-amyl alcohol (1 cm3)] in dry benzene (3 cm3) was added solid PPh3MeI (121 mg, 0.3 mmol) under argon. A solution of norprezizanone 10 (15 mg, 0.075 mmol) in benzene (2 cm3) was added to the above yellow solution, and the resultant mixture was refluxed for 4 h, J. CHEM. SOC. PERKIN TRANS. I 1994 then was cooled, and the usual work-up followed by chromatography afforded prezizaene 4 (1 2 mg, 78%). A solution of prezizaene 4 (10 mg, 0.05 mmol) in dry THF (1 cm3) at 0°C under argon was treated with 0.6 mol dm-3 BH3-THF(0.17cm3, 0.1 mmol).After being stirred for 30 min at 0 "C,the reaction mixture was allowed to warm to room temp. After stirring of the mixture for 2 h, water was added carefully, followed by aq. NaOH (4 mg, 0.1 mmol) and 30% aq. H,O, (0.023 cm3, 0.2 mmol). After being stirred for a further 30 min, the reaction mixture was worked up as usual. Jinkohol I1 6 was obtained after short column chromatography (8 mg, 72%), vmax/cm 3320; 6,(200 MHz) 0.75 (3 H, s, Me), 0.89 (3 H, d, J 7, 2-Me), 1.00 (3 H, s, Me), 1.02-1.97 (13 H, m), 2.39 (1 H, br s, 8-H),3.52(1 H,t,J10.2,CH2OH)and3.77(1H,dd,Jl0.5and 3.5,CH20H). Acknowledgements We thank Professor Kenji Mori of Tokyo University for kindly providing the spectra of norprezizanone. We wish to express our thanks to Professor K. Venkatesan and Dr.J. Narasimha Murthy of our department for the X-ray crystal structure of compound 22. One of us (N. S.) thanks the UGC, New Delhi for a fellowship. The Sophisticated Instrumental Facility (SIF) at the IISc campus is acknowledged for recording the 400 MHz NMR spectra. References 1 Part 14, P. S. Shanker and G. S. R. Subba Rao, Tetrahedron Lett., 1994,35, 5055. 2 R. Sakuma and A. Yoshikoshi, Chem. Commun., 1968,41. 3 I. C. Nigam, H. Komae, G. A. Neville, C. Radecka and S. K. Paknikar, Tetrahedron Lett., 1968, 2497, and references cited therein; R. M. Coates, R. F. Farney, S. M. Johnson and I. C. Paul, Chem. Commun., 1969,999. 4 F. Kido, H. Uda and A. Yoshikoshi, Tetrahedron Lett., 1967,2815; 1968, 1247.5 N. H. Andersen and M. S. Falcone, Chem. Ind. (London), 1971, 62. 6 T. Nakanishi, E. Yamagata and K. Yoneda, J. Chem. Soc., Perkin Trans. 1, 1983,601. 7 N. H. Andersen, Phytochemistry, 1970,9, 145. 8 D. F. MacSweeney, R. Ramage and A. Sattar, Tetrahedron Lett., 1970,557. 9 (a)F. Kido, H. Uda and A. Yoshikoshi, J. Chem. Soc., Perkin Trans. 1, 1972, 1755; (b) D. F. MacSweeney and R. Ramage, Tetrahedron, 1971,27, 1481; (c) R. M. Coates and R. L. Sowerby, J. Am. Chem. SOC.,1972,94,5386;(d)E. Piers and J. Banville, J. Chem. Soc., Chem. Commun., 1979, 1138; (e) P. R. Vettel and R. M. Coates, J. Org. Chem., 1980,45,5430; (f)A. J. Barker and G. Pattenden, J. Chem. Soc., Perkin Trans. I, 1983, 1901; (g) E. Piers, M. Jean and P. S. Marrs, Tetrahedron Lett., 1987, 28, 5075; (h) K. Sakurai, T. Kitahara and K. Mori, Tetrahedron, 1990,46,761. 10 K. PramodandG. S. R. SubbaRao, J. Chem. Soc., Chem. Commun., 1982,762. 1I S. Janaki, Ph.D. Thesis, Indian Institute of Science, Bangalore, 1988. 12 N. Selvakumar and G. S. R. Subba Rao, Tetrahedron Lett., 1993,34, 7789. 13 E. J. Corey, N. M. Weinshenker, T. K. Schaaf and W. Huber, J. Am. Chem. Soc., 1969,91, 5675. 14 M. A. Qasseem, N. A. J. Rogers and A. A. Othman, Tetrahedron, 1968,24,4535. 15 R. B. Woodward, A. A. Patchett, D. H. R. Barton, D. A. J. Ives and R. B. Kelly, J. Am. Chem. SOC., 1954,76, 2852. 16 W. S. Johnson, R. Pappo and W. F. Johns, J.Am. Chem. Soc., 1956, 78,6339; W. Parker, R. Ramage and R. A. Raphael, J. Chem. Soc., 1962, 1558. 17 A. P. Kraphcho and A. J. Lovey, Tetrahedron Lett., 1973,957. 18 H. J. Reich, J. M. Renga and I. L. Reich, J.Am. Chem. Soc., 1975,97, 5434. 19 G. H. Posner, Org. React., 1972, 19, 1. 20 B. S. Huang, E. J. Parish and D. H. Miles, J. Org. Chem., 1974,39, 2647. 21 W. A. Kinney, M. J. Coghlan and L. A. Paquette, J.Am. Chem. SOC., 1985,107, 7352. 22 D. H. R. BartonandS. W. McCombie, J. Chem. Soc., Perkin Trans. I, 1975, 1574. 23 For a detailed general note, see G. S. R. Subba Rao and K. V. Bhaskar, J. Chem. Soc., Perkin Trans. 1, 1993,281 3. Paper 41028525 Received 13th May 1994 Accepted 3 1st May 1994
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