Iridium Phosphite-Oxazoline Catalysts for the Highly Enantioselective Hydrogenation of Terminal Alkenes

摘要

A modular library of readily available phosphite-oxazoline ligands (L1-L16a-f) has been successfully applied for the first time in the Ir-catalyzed asymmetric hydrogenation of a broad range of highly unfunctionalized 1,1,-disubstituted terminal alkenes. Enantioselectivities up to >99% and full conversions were obtained in several 1,1 -disubstituted alkenes, including substrate classes that have never been asymmetrically hydrogenated before (i.e., 1,1-heteoraryl-alkyl, 1,1-diaryl, trifluoromethyl, etc.). The results indicated that these catalytic systems have high tolerance to the steric and electronic requirements of the substrate and also to the presence of a neighboring polar group. The asymmetric hydrogenations were also performed using propylene carbonate as solvent, which allowed the Ir catalyst to be reused and maintained the excellent enantioselectivities.