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

Racemic dirhodium(II) complexes derived from orthometalated aryl phosphines, Rh 2 (O 2 CCH 3 ) 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 Rh 2 (protos) 4 and Rh 2 (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.