Enantioselective Imine Reduction Catalyzed by Phosphenium Ions

Abstract

The first use of phosphenium cations in asymmetric catalysis is reported. A diazaphosphenium triflate, prepared in two or three steps on a multi-gram scale from commercially available materials catalyzes the hydroboration or hydrosilation of cyclic imines with enantiomeric ratios of up to 97:3. Catalyst loadings are as low as 0.2 mole percent. Twenty-two aryl/heteroaryl pyrrolidines and piperidines were prepared using this method. Imines containing functional groups such as thiophenes or pyridyl rings that can challenge transition metal catalysts were reduced employing these systems.