Asymmetric cyclopropanation of styrenes catalyzed by metal complexes of D₂-symmetrical chiral porphyrin: Superiority of cobalt over iron

(Chemical Equation Presented) The cobalt(II) complex of D ₂-symmetric chiral porphyrin [Co(1)] is an effective catalyst for highly diastereoselective and enantioselective cyclopropanation of a broad range of styrene derivatives under mild conditions. Dimerization of diazo compounds, a common side reaction in metal-mediated carbene transfer processes, is minimized in a cobalt porphyrin-based system, obviating the need to employ excess substrates and slow addition of diazo compounds. The high catalytic activity and selectivity of [Co(1)] evidently resulted from the appropriate combination of the cobalt ion and the chiral porphyrin 1 as the use of iron(III) complex of the same ligand [Fe(l)Cl] afforded the desired cyclopropane products in low yields and poor enantioselectivity.