Chiral Phosphoric Acid-Catalyzed Enantioselective Phospha-Michael-Type Addition Reaction of Diarylphosphine Oxides with Alkenyl Benzimidazoles

An enantioselective phospha-Michael-type addition reaction of diarylphosphine oxides with alkenyl benzimidazoles was demonstrated using a chiral phosphoric acid as the chiral Bronsted acid catalyst. Addition products having phosphorus and benzimidazole units were formed in high yields with excellent enantioselectivities in most cases. The reduction of the phosphine oxide unit in the addition product afforded the corresponding chiral phosphine, which is a potential benzimidazole-based chiral P,N-ligand, without loss of enantiomeric excess.