α-Thio-substituted ketones as precursors of olefins via oxathiolanes: α-methoxybenzyl as protecting group

Abstract

A number of routes to 2-(α-methoxybenzylthio) ketones (3) have been explored with a view to their use as precursors of substituted 2-phenyl-1,3-oxathiolanes. The most successful preparation of compounds (3; R¹= Ph) and (3; R¹= Me) involved the in situ generation of the appropriate α-mercapto ketone (10) from an α-oxo dithiocarbonate and alkylation with α-methoxybenzyl chloride. Lithium aluminium hydride reduction of ketone (3; R¹= Ph) followed by cyclisation to 2,5-diphenyl-1,3-oxathiolane (11) provided a prototype for the approach outlined in Scheme 1 but Grignard and organolithium reagents did not react clearly with ketone (3) to give a general route to protected β-mercapto alcohols.

Treatment of the β-oxo dithiocarbamate (13; R¹= Ph) with base and alkyl halide under phase-transfer catalysis conditions gave the enol derivative (14) by sulphur to oxygen migration followed by alkylation at sulphur.