Cinchona-alkaloid-derived NN ligands for ruthenium catalyzed asymmetric hydrogenation of ketones.

A range of cinchona-alkaloid-derived NN ligands bearing N-H were employed for the asymmetric hydrogenation of ketones. By substituting N-H of the ligands, we demonstrated that the N-H moiety was essential for asymmetric hydrogenation and that without the N-H moiety asymmetric hydrogenation could not proceed, based on which a proposed mechanism is discussed. The effectiveness of the optimal ligand was evaluated on various aromatic and α,β-unsaturated ketones, producing the corresponding alcohols with up to 98.8% ee and good yields.