High stereocontrol in aldol reaction with ketones: Enantioselective synthesis of beta-hydroxy gamma-ketoesters by ester enolate aldol reactions with 2-acyl-2-alkyl-1,3-dithiane 1-oxides

The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lac tones, proceeds with a high degree of stereocontrol at both carbonyl and en olate prochiral centers, the stereocontrol mainly determined by the configu ration of the sulfoxide sulfur atom. The sense of induced stereochemistry o bserved for ester enolates is different from that seen for lactone enolates . Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substitut ed beta-hydroxy-gamma-ketoesters.