Cyclopropanation of an Alkene by a Carbenoid (CH2I2-Zn)
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A carbene associated with a metal is called a carbenoid e.g. the Simmons-Smith reagent formed by insertion of zinc into diiodomethane. The reactions of this reagent are strongly directed by hydroxyl groups in the substrate. The zinc coordinates with the alcohol substituent and directs cyclopropanation cis to the hydroxyl group.