Asymmetric aldol addition of aldehydes to a difluoroketene silyl acetal catalyzed by chiral Lewis acids

Article abstract of DOI:10.1016/S0040-4020(97)00683-2

Aldol reaction of aldehydes with difluoroketene ethyl trimethylsilyl acetal (1) in the presence of a substoichiometric amount of chiral Lewis acid 2 or 3 provides the corresponding α,α-difluoro β-hydroxy esters 4-12 with high enantioselectivities (up to 98% ee). Reaction temperature has a great influence on the enantiofacial selection of aldehydes; the reactions of benzyloxyacetaldehyde catalyzed by Lewis acid 2 at -78 and -30°C gave the (+)- and (-)-α,α-difluoro β-hydroxy esters 7 in optical yields of 98% and 85%, respectively.