Enantioselective syntheses of substituted γ-butyrolactones

Article abstract of DOI:10.1002/jccs.200000006

The previously described chiral 2-acyloxathianes 5 (Scheme I) are used in two different enantioselective syntheses of γ-butyrolactones. In one synthesis, Grignard addition, cleavage and reduction to carbinols RR'C(OH)CH₂OH is followed by tosylation, malonate homologation, lactonization, and removal of the carbomethoxy group to give optically active γ-lactones. A modification of this synthesis (Scheme I) leads to optically active α-methylene-γ-lactones. In the second synthesis, reaction of a bromomagnesium enolate with ketones 5 leads to β-hydroxyesters, which, by appropriate sequences of reduction and cleavage (Scheme II) are converted to optically active α- or β-hydroxy-γ-lactones.