Organocatalyzed Enantioselective Conjugated Addition of Sodium Bisulfite to β-Trifluoromethyl-α,β-unsaturated Ketones.

An efficient organocatalyzed enantioselective conjugated addition of sodium bisulfite to β-trifluoromethyl-α,β-unsaturated ketones using a cinchona alkaloid-derived squaramide catalyst is presented. A series of optically active sulfonic acids, bearing a tertiary stereocenter connecting a CF ₃ group and a SO ₃ H group, were obtained in excellent yields with high enantioselectivities (up to 99% yield and 97% ee) under mild conditions. This method will provide an efficient, economic, and green route to access chiral sulfonic acid compounds.