Synthesis of Optically Active Lactones and 3-Cyclopentenone from Optically Active 3,3-Dialkyl-4-thianones

Abstract

Abstract 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-thianimines with methyl vinyl ketone or methyl acrylate. The diketones 3 were then transformed into new heterocycles 5 by base-induced cyclization. 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 analysis. Desulfurization of the lactone (−)-6b using nickel boride afforded the corresponding lactone (+)-9. A synthesis of optically active 2-alkyl-2-methyl-3-cyclopentenone (S)-(+)-15 via the Ramberg–Bäcklund reaction from the keto ester (R)-(+)-4a was also accomplished.