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

Add time:08/10/2019    Source:sciencedirect.com

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.

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