Stereoselective reduction of ketones by histidine-alkoxysilane complexes: The role of imidazole in nucleophilic substitution at silicon

The reduction of carbonyl compounds with transient, hypervalent silicon hydrides is described. Trialkoxysilanes, upon activation by a catalytic amount of lithium imidazolide or the mono or dilithium salt of histidine, but not by neutral imidazole or histidine, reduced the carbonyl groups of various ketones. Enantiomerically enriched product alcohols were recovered in good to excellent yield (70 – 95%) with e.e.'s ranging from 5–75% when catalyzed by histidine derivatives.