Solphos: A New Family of Efficient Biaryl Diphosphine Ligands

Solphos (7,7′‐bis(diarylphosphino)‐3,3′,4,4′‐tetrahydro‐4,4′‐dimethyl‐8,8′‐bis‐2H‐1,4‐benzoxazine) is a new modular atropisomeric biaryl ligand with a very attractive activity profile. A technically feasible synthesis is described allowing the synthesis of various derivatives of enantiopure ligand on a technical scale. Very good catalytic performances have been demonstrated for the following transformations: Ru‐catalyzed hydrogenation of various β‐keto esters (95–99 % ee, s/c up to 100 000), of acetyl acetone (>99 % ee, dl/meso>98:2), and of an exocyclic α,β‐unsaturated acid (98.6 % ee, s/c 250). In several cases, the nature of the PAr2 moiety had a significant effect on the enantioselectivity. Furthermore, Rh and Ir Solphos complexes achieved high enantioselectivities for a novel synthesis of 3,3‐disubstituted phthalides and the reductive coupling of alkynes with N‐sulfonyl imines, respectively. Effective for Ru‐catalyzed hydrogenation: Solphos is a new modular atropisomeric biaryl ligand with an attractive activity profile. Very good catalytic performances have been demonstrated for the Ru‐catalyzed hydrogenation of β‐keto esters (95–99 % ee, s/c up to 100 000), of acetyl acetone (>99 % ee, dl/meso>98:2), and of an exocyclic α,β‐unsaturated acid (98.6 % ee, s/c 250). In several cases, the nature of the PAr2 moiety has a significant effect on the enantioselectivity.