This Simmons-Smith reaction begins with the halogen-metal exchange between diiodomethane (methylene iodide) and zinc (in a zinc/copper alloy) to produce a reactive intermediate organometallic carbenoid. This carbenoid then undergoes cycloaddition with the pi bond of cyclohexene (an alkene) to produce the cyclopropane ring of bicyclo[4.1.0]heptane.