Synthesis of Cyclopropanes using RZnX (The Simmons-Smith reaction)

Summary

• This is the most important reaction involving an organozinc reagent.
• Also known as the Simmons-Smith reaction
• The iodomethyl zinc iodide is usually prepared using Zn activated with Cu.
• The iodomethyl zinc iodide reacts with an alkene to give a cyclopropane.
• The reaction is stereospecific with respect to the alkene (mechanism is concerted).

Substituents that are trans in the alkene are trans in the cyclopropane etc.

• Addition reactions of alkenes (Ch 6)

MECHANISM OF THE SIMMONS-SMITH REACTION
Step 1: A concerted reaction : both new C-C are formed simultaneously. Best viewed as the nucleophilic C=C causing loss of the iodide leaving group and the electrons from the nucleophilic C-Zn bond being used to form the other C-C bond.