Cyclopropanation

Abstract Catalyzed reactions are quite usually the most versatile and direct way to cyclopropanes. Central to all synthetic efforts is the ability to control the relative and absolute stereochemistry around the cyclopropane ring. Recent developments in olefin cyclopropanation with transition metal complexes based mostly on palladium, copper, and rhodium are summarized where the carbene precursor is a diazocompound. Related metal‐mediated cyclopropanation reactions such as the Kulinkovich hydroxycyclopropanation, the Simmons–Smith reaction, and assymetric variations thereof are also considered, as well as less studied synthetic methods that involve cyclopropanation with electron holes, selenium‐assisted cyclopropanation, and cyclopropanation with lithiated sulfones. Recent breaktroughs in enantioselective cyclopropanation of double bonds with chiral copper and rhodium catalysts are compared and illustrated with different examples, inter alia for the synthesis of natural products. Related reactions such as the cyclopropenation of carbon–carbon triple bonds and the aziridination of double bonds can be promoted with the same families of catalysts. These methodologies offer ready synthetic entries into many new molecules, including natural compounds.