Synthesis of both enantiomers of optically pure saturated and α,β-unsaturated γ-substituted γ-lactones from chiral sulphoxides. X-Ray molecular structure of (3R,4S)-4-methyl-4-t-butyl-3-(p-tolylthio)butanolide and of (3R,4R)-4-(cyclohex-1-enyl)-4-methyl-3-(p-tolylthio)butanolide

Abstract

The lithium carbanions of optically pure (+)-(R)-p-tolyl alkyl sulphoxides (5) reacted with lithium bromoacetate and gave (+)-(R)-3-(p-tolylsulphinyl)carboxylic acids (3). Their dimetallation produced a chiral homoenolate dianion equivalent (6) which added to carbonyl compounds (4) to furnish sulphinyl lactones (7) in moderate chemical and optical yields. However, single diastereoisomers of these compounds could be easily separated through chromatography, and were transformed in high yields into both enantiomers of optically pure saturated and α,β-unsaturated γ-lactones (1) and (2). Relative and absolute stereochemistry of all the products obtained was determined through c.d., nuclear Overhauser effects, and X-ray analyses.