Versatile Donor‐Acceptor Cyclopropenes in Metal Carbene Transformations

Abstract Select transition metal compounds catalyze metal vinylcarbene formation from cyclopropenes, and their documented reactions include both intermolecular and intramolecular C−H insertion and cyclopropanation, as well as [3+3]‐cycloaddition. Although known to undergo carbene‐like transformations for decades, the uses of cyclopropenes as reactive alternatives to diazo compounds under mild conditions has been limited. However, recently developed donor‐acceptor cyclopropenes that are conveniently accessed from enoldiazoacetates and enoldiazoacetamides are effective metallo‐vinylcarbene precursors. They provide entry to highly stereoselective metal carbene transformations under reaction conditions that are milder than those required for dinitrogen extrusion from diazo compounds.