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 beta-keto esters (95-99 % ee, s/c up to 100,000), of acetyl acetone (>99 % ee, dl/meso>98:2), and of an exocyclic alpha,beta-unsaturated acid (98.6 % ee, s/c 250). In several cases, the nature of the PAr(2) 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.