Broader, greener, and more efficient: recent advances in asymmetric transfer hydrogenation.

Asymmetric transfer hydrogenation has become a practically useful tool in reduction chemistry in the last decade or so. This was largely triggered by the seminal work of Noyori and co-workers in the mid-1990s and is driven by its complementing chemistry to hydrogenation employing H(2). This Focus Review attempts to present a "holistic" overview on the advances in the area, focusing on the achievements recorded around the last three years. These include more-efficient and "greener" metal catalysts, catalysts that enable hydrogenation as well as transfer hydrogenation, biomimetic and organocatalysts, and their applications in the reduction of C==O, C==N, and C==C bonds. Also highlighted are efforts in the development of environmentally benign and reusable catalytic systems.