Enantioselective copper-catalyzed conjugate addition of diethylzinc to enones using new chiral P,N ligands composed of (S)-2-alkyl-2-aminoethylphosphines and α-substituted pyridines

New P,N ligands prepared from (S)-2-alkyl-2-aminoethylphosphines and α-substituted pyridines are efficient chiral ligands for the copper-catalyzed conjugate addition of diethylzinc to 2-cyclohexen-1-one and chalcone. The best result (90–91% ee) for the cyclohexenone was obtained with Cu(OTf)2 (0.7–1 mol%) and a P,N ligand 4 derived from (S)-1-(diphenylphosphino)-3-methyl-2-butanamine and 6-methylpyridine-2-carboxaldehyde.