First Asymmetric Hydrogenation Using Homogeneous Chiral Nickel Catalysts through DKR

摘要

Asymmetric hydrogenation is a powerful synthetic tools for the preparation of optically active compounds on an industrial scale in which precious transition metals, Rh, Ir, and Ru, play a crucial role as the central metal of the homogeneous catalyst. These metals, however, are expensive rare metals and their uses are anticipated to be limited by depletion of natural resources in the future. Hence, the investigation and development of sustainable methods using abundant and cheap base transition metals is desirable. Recently, we have reported the efficient asymmetric hydrogenation of α-amino-β-keto esters using chiral ruthenium, rhodium, and iridium-catalysts in the enantio- and diastereoselective synthesis of anti-β-hydroxy-α-amino acids through dynamic kinetic resolution (DKR). During the course of our studies, we envisioned the new potential of nickel, one of the base transiotion metals, in this asymmetric hydrogenation. Although several asymmetric hydrogenations using Raney nickel, a heterogeneous catalyst, with chiral modifier have been developed to date, the homogeneous nickel-catalyzed asymmetric hydrogenation has received no attention for a long time. We now describe the first and successful asymmetric hydrogenation using homogeneous chiral nickel catalysts in the stereoselective synthesis of anti-β-hydroxy-α-amino acids from chirally labile α-amino-β-keto esters.