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 [(Sa,Sc)-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 [(Sa,Sc)-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 [(Sa,Sc)-2] proved to be the most selective ligand. Substantially lower ees were obtained with the mismatched diastereomer (Ra,Sc)-1b and with the N-phenyl-substituted ligand 1c, missing a second element of chirality.