Transition Metal‐Catalyzed Carbene Coupling Reaction

Comprehensive Summary Transition‐metal‐catalyzed carbene transfer reactions have emerged as a robust and versatile strategy in organic synthesis. Conventional carbene transfer processes primarily encompass C–H bond insertion, cyclopropanation, and ylide formation, which have found extensive applications both in academic research and industrial settings. A prominent example includes the Rh(II)‐catalyzed intramolecular N–H insertion employed in the synthesis of β‐lactam antibiotics such as thienamycin, as well as asymmetric cyclopropanation utilized in the production of chrysanthemate‐based insecticides. Over the past decade, a novel class of transition‐metal‐catalyzed transformations involving carbene precursors has gained significant attention. In these reactions, diazo compounds—or their precursors such as N ‐tosylhydrazones—serve as cross‐coupling partners for the construction of C–C single or C=C double bonds. The transformations developed thus far in this field are summarized in the accompanying figure. These processes typically proceed via metal–carbene intermediates followed by migratory insertion steps, enabling efficient bond formation under either redox‐neutral or oxidative conditions. The broad compatibility of various carbene precursors and coupling partners has greatly enhanced the synthetic utility of this approach. This carbene‐based coupling strategy has demonstrated wide applicability, with numerous transition metals—including Pd, Cu, Rh, Ni, Co, and Ir—proving effective as catalysts. Moreover, the substrate scope has expanded beyond diazo compounds to include other carbene sources, and diverse cascade processes have been designed based on carbene migratory insertion. In addition, this methodology has been integrated with C–H functionalization, fluorine chemistry, and more recently, metal‐hydride‐mediated transformations. Its utility extends from the synthesis of complex molecules to the development of functional polymeric materials. Concurrently, asymmetric versions of carbene cross‐coupling reactions are being actively explored, although considerable challenges remain in this area. This review summarizes the historical development and recent advances in transition‐metal‐catalyzed carbene transfer reactions, with a focus on emerging coupling strategies and their synthetic applications. Key Scientists