Chiral Dirhodium(II) Catalysts with Orthometalated Aryl Phosphine Ligands: Synthesis and Application for Enantioselective C−H Insertion of α-Diazo Ketones

Abstract

Racemic dirhodium(II) complexes derived from orthometalated aryl phosphines, Rh2(O2CCH3)2(pc)2 (pc = orthometalated phosphine, with head-to-tail arrangement) (1−7), are isolated as pure enantiomers by conventional resolution methods. They are the first examples of dirhodium(II) chiral catalysts without chiral ligands. These compounds have been used in the cyclization of α-diazo ketones; the influence of catalyst and substrate on enantioselectivity is studied. Results are compared with those obtained for reactions catalyzed by Rh2(protos)4 and Rh2(protos)2(pc)2 [ProtosH (8) = N-(4-methylphenylsulfonyl-l-proline] (9−22). Only catalysts 1−7 afford a high level of enantioselectivity in the synthesis of carbocycles from α-diazo ketones.