Trichlorosilane-mediated stereoselective reduction of carbon-nitrogen double bonds

The reduction of C=N bonds represents a powerful and widely used transformation allowing new nitrogen-containing stereocenters to be generated. Chiral amino groups are ubiquitous in a variety of bioactive molecules such as alkaloids, natural products, drugs, and medical agents, so the development of a catalytic stereoselective process for the preparation of enantiomerically enriched amines through ketoimine reduction is attracting increasing interest, especially in view of future industrial applications. Great efforts to develop efficient organocatalytic methods to perform enantioselective imine reductions and reductive amination processes have recently been made. In the last few years, trichlorosilane-mediated reductions have received constantly increasing attention because the potential to generate chiral catalysts for imine reduction simply by coordination of HSiCl3 with a chiral Lewis base has allowed the development of several efficient organocatalytic systems. Here we offer a complete overview of different chiral promoters of stereoselective reductions with trichlorosilane, classified as N-formyl derivatives, which may be considered historically the first class of compounds developed as chiral activators of trichlorosilane, picolinamide derivatives, and miscellaneous compounds presented in that order. C=N bond reduction is a powerful, widely used transformation allowing new nitrogen-bearing stereocenters to be created. Generation of chiral catalysts for imine reduction simply by coordination of HSiCl3 with chiral Lewis bases has allowed the development of several efficient organocatalytic systems. An overview of chiral promoters for stereoselective C=N reductions with HSiCl3 is provided.