An enantioselective sulfa-Michael addition of alkyl thiols to α,β-unsaturated 2-acyl imidazoles catalyzed by a bifunctional squaramide

An enantioselective catalytic sulfa-Michael addition of alkyl thiols to α,β-unsaturated 2-acyl imidazoles using bifunctional organocatalysts is reported. The methodology works efficiently with low catalyst loading (1 mol%) to furnish sulfa-Michael adducts in excellent yields (up to 98%) and high enantioselectivities (up to 92% ee). A transition state model has been proposed to explain the stereochemical outcome of the reaction.