The Simmons-Smith reaction is a chemical process used to convert alkenes into cyclopropanes. This reaction involves the use of a zinc-copper couple and iodomethane to generate a carbenoid species, which then adds to the double bond of the alkene. The result is a three-membered cyclopropane ring, a useful structure in organic synthesis. This reaction is valued for its ability to create cyclopropanes with high stereoselectivity and efficiency. It is particularly useful in the synthesis of complex organic molecules, making it a significant tool in the field of organic chemistry.