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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.