Diastereoselective synthesis of γ-hydroxy α,β-epoxyesters and their conversion into β-hydroxy α-sulfenyl γ-butyrolactones

Abstract

The diastereoselectivity of the nucleophilic epoxidation of γ-hydroxy-α,β-unsaturated esters has been studied. The γ-hydroxy-α,β-unsaturated esters were obtained through treatment of ethyl ( E)-4-oxo-2-butenoate with the corresponding Grignard reagent and were used as a racemic mixture. The resulting γ-hydroxy α,β-epoxyesters were treated with thiophenol for transformation into α-phenylsulfanyl trisubstituted γ-butyrolactones. The syn, syn-lactones isomerize easily in basic media into the syn, anti structures. In order to explain this interconversion, a retroaldol–aldol sequence has been proposed and a sulfur–oxygen interaction has been invoked to explain the syn stereochemical preference of the α-sulfured aldols resulting from the intramolecular aldol reaction.