Cyclopropyl Carbene: the Generation and Reactions †

Comprehensive Summary Cyclopropyl carbenes represent a unique and synthetically powerful class of reactive intermediates, combining the high energy of a carbene center with the intrinsic ring strain of the cyclopropane moiety. This review provides a systematic overview of recent advances in their generation, reaction behavior, and synthetic applications. Four primary precursor classes are discussed. Cyclopropyl diazo compounds serve as the most direct and widely employed precursors, enabling precise control over carbene reactivity under photochemical, thermal, or transition metal‐catalyzed conditions. Cyclopropyl N ‐tosylhydrazones offer a safer and more stable alternative, allowing in situ carbene generation and facilitating diverse transformations, including ring‐expansion and palladium‐catalyzed cross‐coupling reactions. Cyclopropyl‐tethered allenyl ketones, upon transition metal catalysis, generate cyclopropyl carbene intermediates that subsequently rearrange to furan‐fused cyclobutenes, which can participate in various cycloadditions or ring‐opening reactions to afford complex polycyclic frameworks. In addition, miscellaneous precursors such as diazirines, methylenecyclopropanes, and cyclopropenes provide complementary strategies for accessing these reactive species. Despite significant progress, challenges remain in achieving broadly applicable and highly stereoselective transformations. Future efforts will focus on the development of novel chiral catalytic systems and the discovery of unprecedented reactivity modes, which are expected to further expand the synthetic utility of cyclopropyl carbenes in organic synthesis.