Simmons-Smith Cyclopropanation

In 1958, Howard Ensign Simmons Jr. and Ronald D. Smith stereospecifically converted unfunctionalized alkenes such as cyclohexene to cyclopropanes using diiodomethane (CH₂I₂) in the presence of a zinc-copper couple. This reaction proved to be general, and has since become an important method of preparing cyclopropanes; it is known today as the Simmons-Smith cyclopropanation.

The zinc-copper couple can be prepared by reacting zinc powder with copper sulfate solution. However, a zinc-silver couple often gives better yields and shorter reaction times. The use of diethylzinc with diiodomethane also gives excellent results, and is known as the Furukawa modification. The use of iodo- or chloromethyl samarium iodide for the cyclopropanation of allylic alcohols in the presence of other olefins is known as the Molander modification.

The Simmons-Smith cyclopropanation reaction was used in the total synthesis of the antimitotic agent (+)-curacin A by the team of Shigeo Iwasaki to generate the cyclopropane ring.