A Comparison of (Chloromethyl)- and (Iodomethyl)zinc Cyclopropanation Reagents

A study comparing the rate of cyclopropanation of a range of olefins using (chloromethyl)- and (iodomethyl)zinc reagents is described. The (chloromethyl)zinc reagent derived from diethylzinc and chloroiodomethane is generally more reactive than the (iodomethyl)zinc analogue. The use of 1,2-dichloroethane as the solvent for these reactions was shown to be a crucial factor necessary to achieve clean, rapid, high-yielding cyclopropanations. The well-known directing effect of proximal oxygen substituents on the stereochemical outcome of “Simmons-Smith” cyclopropanations was shown to hold for the (chloromethyl)zinc reagent as well. The diethylzinc/chloroiodomethane reagent system in 1,2-dichloroethane should prove to be a valuable alternative to traditional (iodomethyl)zinc-based cyclopropanation reagents.