Efficient approach for the design of effective chiral quaternary phosphonium salts in asymmetric conjugate additions

An efficient approach for the design of chiral quaternary phosphonium bromides as chiral phase-transfer catalysts was demonstrated. A catalyst library of phosphonium salts with various structures was readily constructed using commercially available chiral phosphines as catalyst precursors, and an optimized catalyst was successfully applied to highly enantioselective conjugate additions under base-free phase-transfer conditions with low catalyst loading.