Highlights of Transition Metal-Catalyzed Asymmetric Hydrogenation of Imines

This Review deals with the asymmetric hydrogenation and asymmetric transfer hydrogenation of imines and some nitrogen-containing heteroaromatic compounds to afford amines. Hydrogenation and transfer hydrogenation are covered in separate sections. Particular attention is devoted to the substrates, since this reaction is highly substrate dependent. In this way the general structural trends in imine hydrogenation are presented, highlighting the more challenging substrates. Since hydrogenation of acyclic and cyclic (including heteroaromatic) imines have some different features they are also presented separately. The catalytic systems are classified according to the metal, and focus on the most successful catalytic systems and metal-ligand combinations. The catalytic cycles for these hydrogenation processes are also proposed.