Versatile Donor-Acceptor Cyclopropenes in Metal Carbene Transformations

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.