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(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 ol-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 alpha -diazo ketones.