Ru-Catalyzed Asymmetric Reductive Amination of Benzyl Ketones: Asymmetric Control Enabled by Synergistic Interaction of Both Chiral Bisphosphine and Chiral Amino-Acid Ligands

Chiral methylbenzylamines and arylbenzylamines are important structural motifs that are widely present in many bioactive compounds and drug molecules. In this study, we applied readily available ruthenium complexes, comprised of a bisphosphine and two chiral amino acid anionic ligands, in asymmetric reductive amination of benzyl ketones with ammonium salts for the first time. Excellent enantioselectivities (up to 99% ee) have been achieved by merely fine-tuning the amino acid structure, thereby decreasing the need for more expensive bisphosphine ligands. We anticipate that this new method will find broad applications in organic synthesis, especially in the preparation of chiral pharmaceutical intermediates.