Enantioselective addition of diethylzinc to N-diphenylphosphinoylimines employing N,N-dialkyl-1,2-diphenyl-2-aminoethanols as chiral ligands

By fine-tuning the substituents on the nitrogen of (1S,2R) and (1R,2S)-1,2-diphenyl-2-aminoethanols, a chiral ligand 2b was obtained, which showed excellent enantioselectivity, with up to 94% e.e, for the asymmetric addition of diethylzinc to N-diphenylphosphinoylimines 1. In one example, the optically active amide 3c was converted into a new amine 5 with 98% e.e. by a reaction sequence involving Suzuki coupling and hydrolysis without racemization.