Catalytic Enantioselective Aldol Reactions of Unprotected Carboxylic Acids under Phosphine Oxide Catalysis

The first catalytic enantioselective aldol reaction of various unprotected carboxylic acids is described. In the presence of a chiral bis(phosphine oxide) as a Lewis base catalyst, carboxylic acids were activated with silicon tetrachloride to form the corresponding bis(trichlorosilyl)enediolates in situ, which subsequently underwent an aldol reaction with an aldehyde or a ketone to produce beta-hydroxycarboxylic acids in high enantioseledivities of up to 92% ee.