Difluorocarbene (: CF 2 ) as a Minimal Perfluorocarbon linker for the Synthesis of gem ‐Difluoromethylenated Compounds ( G 1 ‐ CF 2 ‐ G 2 , G 1 , G 2 ≠ H, F): From 2019 to 2025

Comprehensive Summary This review systematically details the significant advances from 2019 to 2025 in utilizing difluorocarbene (:CF 2 ) as a minimal perfluorocarbon linker for the efficient synthesis of gem ‐difluoromethylenated compounds (G 1 ‐CF 2 ‐G 2 , G 1 , G 2 ≠ H, F). As the smallest perfluorocarbon linker, :CF 2 has evolved beyond a traditional C1 synthon into a versatile bipolar connective scaffold, enabling modular assembly through innovative methodologies. The progress is systematically categorized into two primary domains: the synthesis of linear and cyclic architectures. For linear molecules, breakthroughs include tunable transition‐metal catalysis ( e.g ., Pd, Cu) that enables controlled three‐component couplings and programmable fluoroalkyl chain elongations, alongside diverse metal‐free strategies utilizing phosphonium ylides, silyl reagents, and oxidative protocols for incorporating heteroatoms (O, S, N, Se, etc .) into the ‐CF 2 ‐ bridge. In cyclic molecule synthesis, beyond the classical [2+1] cycloaddition for the synthesis of gem ‐difluorocyclopropanes, novel annulation paradigms such as [3+1], [4+1], and [1+4] cycloadditions have emerged, providing efficient access to a wide array of medicinally relevant fluorinated heterocycles. Furthermore, complementary difluorocarbene‐like pathways, particularly those employing radical‐based synthons, offer alternative routes for constructing the ‐CF 2 ‐ linkage. Looking forward, the review provides inspiring perspectives, emphasizing the in‐depth fundamental studies of metal‐difluorocarbene coupling reactions, the development of bench‐ stable and externally activated (light, electricity) :CF 2 precursors, the pursuit of enantioselective :CF 2 transfer for constructing chiral G 1 *–CF 2 –G 2 centers, and the exploration of :CF 2 as a repeating linker unit in high‐performance fluorinated polymers and materials. The integration of computational prediction with experimental validation is highlighted as a powerful tool for discovering :CF 2 ‐mediated transformations, while the application of these methodologies in late‐stage diversification of complex pharmaceuticals and agrochemicals underscores their practical utility. This consolidated overview underscores :CF 2 's transformative role as a minimal perfluorocarbon linker in modern synthetic methodology, offering valuable insights for organic, medicinal, and materials chemists to design and access complex fluorinated targets with enhanced efficiency and precision. Key Events Related to Difluorocarbene (:CF 2 ) Chemistry The development of difluorocarbene (:CF 2 ) chemistry has traversed a long journey from a transient reactive intermediate to a powerful synthetic linchpin for constructing G 1 –CF 2 –G 2 architectures. According to our literature survey, the earliest evidence for the generation of :CF 2 dates back to 1933, when it was produced via the high‐temperature pyrolysis of CF 4 [1] and the high‐tension electric discharge decomposition of Cl 2 CF 2 . [2] Since the 1940s, :CF 2 (from ClCF 2 H) has been directly employed in the preparation of polytetrafluoroethylene (Teflon), and ever since, downstream products based on :CF 2 have been widely developed and applied. Concurrently, the discovery and extensive utilization of fluorinated compounds and materials have also spurred the rise and advancement of organofluorine chemistry. [3] Owing to the inherently high reactivity and instability of :CF 2 , synthetic methodologies involving it remained largely unexplored until 1957, when J. Hine successfully captured :CF 2 using sodium methoxide and thiophenoxide to afford the corresponding difluoromethyl (thio)ethers. [4] Subsequently, J. M. Birchall, H. C. Clark, and co‐workers reported the [2+1] cycloaddition of :CF 2 with cyclohexene [5] and tetrafluoroethylene, [6] leading to difluorocyclopropane derivatives. Thereafter, a series of synthetic methods based on free :CF 2 have been continuously developed. In 1978, D. L. Reger and co‐workers reported the first mononuclear metal difluorocarbene complex ([M]=CF 2 , M =Mo), [7] suggesting that [M]=CF 2 may regulate the CF 2 's reactivity. However, although these pioneering discoveries are of great significance, the process of constructing the G 1 –CF 2 –G 2 (G 1 , G 2 ≠ H, F) molecules using :CF 2 was severely hampered by several intrinsic obstacles: harsh reaction conditions (extremely high temperatures or electric discharge), limitations of the available apparatus, [2,8] as well as the tendency of :CF 2 to undergo self‐polymerization and α‐fluoride elimination. [9] Consequently, progress in this area remained sluggish for decades. It was not until the 1990s that a series of reports began to emerge on the use of :CF 2 in consecutive bond‐forming reactions to access both linear and cyclic G 1 –CF 2 –G 2 (G 1 , G 2 ≠ H, F) architectures. [10]