Highly Enantioselective Organocatalytic Sulfa-Michael Addition to α,β-Unsaturated Ketones

A cinchona alkaloid-derived urea was found to be an efficient organocatalyst for catalyzing enantioselective conjugate addition between thiols and various alpha,beta-unsaturated ketones to provide optically active sulfides with high chemical yields (up to > 99%) and enantiomeric excess (up to > 99% ee). The reaction was performed with 0.1 mol % of catalyst in toluene at room temperature. A transition state model has been proposed to explain the stereochemical outcome of the reaction.