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

Abstract

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.