Enantioselective reactions through chiral metal-carbene intermediates

Olefin cyclopropanation with prochiral diazoalkanes, e.g.N2CHC02R, has been found to proceed with high degree of enantioselection (max.88% e.e.) by catalysis of novel cobalt(II) chelates prepared from natural camphor or 8-pinene; viz.bis(camphorquinonedioximato) or bis(nopinoquinonedioximato)cobalt(II).A mechanism involving enantioface selective olefin attack upon transient chiral cobalt-carbene complexes formed from prochiral diazoalkanes was proposed.Chirality at the Co(II) seems tobe an important factor in determining the chirality of the prevailing cyclopropane enantiomeric product.