Highly stereoselective synthesis of enantiomerically pure β-hydroxy-γ-sulfenyl-γ-butyrolactone by asymmetric Pummerer type cyclization

Enantiomerically pure t-butyl 4-sulfinyl-3-silyloxy-butanoate can be transformed stereoselectively in a Pummerer reaction with TFAA into the usual aldehyde or into a cis β-hydroxy-γ-sulfenyl-γ-butyrolactone. Experimental conditions allowing total control of the reaction in favor of either the aldehyde or the γ-butyrolactone are described. The corresponding methyl butanoate led, under the same conditions, only to the aldehyde.