Chiral dirhodium(II) catalysts with ortho-metalated arylphosphine ligands:: Synthesis and application to the enantioselective cyclopropanation of α-diazo ketones

Chiral dirhodium(II) compounds, Rh-2(O2CR)(2)(pc)(2) (pc = ortho-metalated arylphosphine), with a head-to-tail arrangement (1-21) are used in the cyclopropanation of alpha-diazo ketones. The influence of catalyst ligands and substrate structure on enantioselectivity is studied. Temperature and solvent dependence assays are performed, the best ee values being obtained in refluxing pentane. Results compare favorably with those reported in the literature using Ru, Cu, and other Rh(II) catalysts.