Highly Efficient and Versatile Phosphine-Phosphoramidite Ligands for Asymmetric Hydrogenation

A set of novel phosphine-phosphoramidite ligands possessing two elements of chirality have been prepared through a modular synthetic approach. The ligands (11bS)-N-[2-(diphenylphosphino)phenyl]-N-[(S)-1-phenylethyl]dinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepin-4-amine [(S-a,S-c)-1a] and(11bR)-N-[2-(diphenylphosphino)phenyl]-N-[(S)-1-(1-naphthyl)ethyl]dinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepin-4-amine [(S-a,S-c)-1b] are unique in providing enantioselectivities >= 96% ee and >= 94% ee, respectively, in mechanistically distinct hydrogenations of C=C, C=N and C=O double bonds in combination with three different transition metals (rhodium, iridium, and ruthenium, respectively). Particularly remarkable are the enantiomeric excesses up to 97% achieved in the iridium-catalyzed hydrogenation of 2-substituted quinolines, where (11bS)-N-[2-(diphenylphosphino)phenyl]-N-[(S)-1-(naphthalen-1-yl)ethyl]-8,9,10,11, 12,13,14,15-octahydrodinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepin-4-amine [(S-a,S-c)-2] proved to be the most selective ligand. Substantially lower ees were obtained with the mismatched diastereomer (R-a,S-c)-1b and with the N-phenyl-substituted ligand 1c, missing a second element of chirality.