Transition-Metal Catalyzed Carbene Transformations <i>via</i> Ring Strain-Release Processes

Carbenes exhibit high reactivity, enabling versatile molecular modifications with broad applications in pharmaceuticals, agrochemicals and biological chemistry. Diazo compounds have historically served as the one of the most widely applicable precursors for carbene transformations, however, they are limited by inherent instability and explosiveness. In recent years, strain-release strategies involving small, high-energy carbocyclic molecules such as cyclopropenes, bicyclo[1.1.0]butanes (BCBs), [1.1.1]propellane (TCP), methylenecyclopropanes (MCPs), and vinylidenecyclopropanes (VDCPs) have emerged as promising nondiazo type carbene precursors, providing safer and more efficient routes for metal carbene transformations. These strained molecules have expanded the synthetic toolbox through ring strain-release process, enabling transformative applications in drug innovation, pesticide design and material science. This review summarizes recent advances in ring strain-enabled carbene transformations, offering a critical evaluation of current synthetic strategies while identifying unexplored opportunities.