Simmons-Smith Cyclopropanation

Howard E. Simmons and Ronald D. Smith demonstrated that alkenes react with iodomethyl zinc iodide (ICH₂ZnI) to form a three-membered ring. In this reaction, an organozinc compound is synthesized in the presence of an ether solvent such as diethyl ether (Et₂O), which stabilizes the organozinc intermediate. The organozinc compound can be synthesized by treating an alkyl halide with zinc in ether as shown below:

In the Simmons-Smith reaction, diiodomethane (CH₂I₂) is treated with zinc copper couple (Zn-Cu) to yield ICH₂ZnI and subsequently reacted with an alkene to yield a cyclopropane. To prepare Zn-Cu couple, zinc dust is treated with CuCl or CuSO₄. This is a highly stereoselective reaction that results in a cyclopropane product with e same stereochemistry as the starting alkene. The following is an example of cycopropanation of an alkene using ICH₂ZnI, Zn-Cu, and Et₂O

Simmons-Smith Cyclopropanation Mechanism: