Development of Multidentate P,P,N,N-Ligands for Ruthenium-Catalyzed Enantioselective Hydrogenation of 2-Pyridyl Ketones

A series of ferrocene-based chiral multidentate P,P,N,N-ligands were successfully designed and synthesized. They can be directly prepared via a one-step nucleophilic substitution reaction from (S)-1-[(R)-2-(diphenylphosphino)ferrocenyl] ethyl acetate [(S_C,R_FC)-BPPFOAc]. Their ruthenium complexes were used in the asymmetric hydrogenation of 2-pyridyl ketones under mild conditions, the target chiral 1-aryl- or 1-alkyl-(pyridine-2-yl)methanols were obtained with high yields and excellent enantioselectivities. The synthetic utility of this reaction was demonstrated through its utilization in the preparation of key intermediates for a RAS inhibitor and the antihistamine drug Carbinoxamine.