SYNTHESIS OF OPTICALLY-ACTIVE LACTONES AND 3-CYCLOPENTENONE FROM OPTICALLY-ACTIVE 3,3-DIALKYL-4-THIANONES

The Optically active 3,3-dialkyl-4-thianones 3 and 4 were prepared in moderate yields with about 90% enantiomeric purity using an asymmetric process involving a Michael-type alkylation of chiral 3-alkyl-4-thian imines with methyl vinyl ketone or methyl acrylate. The diketones 3 we re then transformed into new heterocycles 5 by base-induced cyclizatio n. 3-Methyl- and 3-allyl-3-(2-methoxycarbonylethyl)-4-thianone ((+)-4a and (+)-4b) were converted into the bicyclic lactones (-)-6 and (-)-7 , respectively. The stereochemistry of the sulfone (+)-8 derived from the lactone (-)-6a was determined by a X-ray crystal structure analysi s. Desulfurization of the lactone (-)-6b using nickel boride afforded the corresponding lactone (+)-9. A synthesis of optically active alkyl -2-methyl-3-cyclopentenone (S)-(+)-15 via the Ramberg-Backlund reactio n from the keto ester (R)-(+)-4a was also accomplished.