Metal-catalyzed cyclopropanations are chemical reactions that result in the formation of a cyclopropane ring from a metal carbenoid species and an alkene. In the Simmons–Smith reaction the metal involved is zinc. Metal carbenoid species can be generated through the reaction of a diazo compound with a transition metal). The intramolecular variant of this reaction was first reported in 1961.  Rhodium carboxylate complexes, such as dirhodium tetraacetate, are common catalysts. Enantioselective cyclopropanations have been developed.