prepared in 32–96% yield by the reaction of olefins with ethylidene iodide and diethylzinc. The reaction is electrophilic, and proceeds stereospecifically. In the case of the reaction with 1,2-disubstituted olefins, cis and transolefins affords cyclopropane derivatives whose configurations with respect to the substituents from original olefins are cis and trans, respectively.