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.