Cinchona-Alkaloid-Derived NNPP Ligands for Iridium-Catalyzed Asymmetric Hydrogenation of Unsymmetrical Benzophenones

A series of novel NNPP ligands based on cinchona alkaloids have been developed for the asymmetric hydrogenation of benzophenones, which contain two phosphorus atoms in identical chemical environments. If one phosphorus atom becomes oxidized and is unable to participate in the coordination process, then the other takes its place to ensure that the asymmetric hydrogenation can be completed successfully. The protocol demonstrates excellent catalytic activity and enantioselectivity of up to 99% with various benzophenones (29 examples), including challenging substrates, such as <i>o</i>-aminobenzophenones.