Summary: A method for the stereoselective synthesis of silyl ketene acetals from a-hydroxy esters is described. Internal quench with excess TMSCl of the lithium enolate at-100" C, which is generated using a hindered base, LTMP, leads to the selective formation of (E)-silyl ketene acetal. In contrast, the deprotonation at-100" C using LHMDS in THF-HMPA (411, followed by treatment with tert-butyldimethylsilyl chloride affords the (Z)-silyl ketene acetal ...
