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Transition-metal catalyzed allylic substitution reactions of alkenes are among the most efficient methods for synthesizing diene compounds, driven by the inherent preference for an inner-sphere mechanism. Here, we present a demonstration of an outer-sphere mechanism in Rh-catalyzed allylic substitution reaction of simple alkenes using gem-difluorinated cyclopropanes as allyl surrogates. This unconventional mechanism offers an opportunity for the fluorine recycling of gem-difluorinated cyclopropanes via C − F bond cleavage/reformation, ultimately delivering allylic carbofluorination products. The developed method tolerates a wide range of simple alkenes, providing access to secondary, tertiary fluorides and gem-difluorides with 100% atom economy. DFT calculations reveal that the C − C bond formation goes through an unusual outer-sphere nucleophilic substitution of the alkenes to the allyl-Rh species instead of migration insertion, and the generated carbon cation then forms the C − F bond with tetrafluoroborate as a fluoride shuttle. Allylic substitution reaction of alkenes has been well-developed, but it has limitations, partly due to the intrinsic predilection for an inner-sphere mechanism. Herein, the authors present an outer-sphere mechanism in Rh-catalyzed allylic substitution reaction of simple alkenes using gem-difluorinated cyclopropanes as allyl surrogates. [ABSTRACT FROM AUTHOR]

Direct synthesis of gem‐difluorinated carbocyclic molecules represents a longstanding challenge in organic chemistry. Herein, a Rh‐catalyzed [3+2] cycloaddition reaction between readily available gem‐difluorinated cyclopropanes (gem‐DFCPs) and internal olefins has been developed, enabling the efficient synthesis of gem‐difluorinated cyclopentanes with good functional group compatibility, excellent regioselectivity and good diastereoselectivity. The resulting gem‐difluorinated products can undergo downstream transformations to access various mono‐fluorinated cyclopentenes and cyclopentanes. This reaction demonstrates the use of gem‐DFCPs as a type of "CF2" C3 synthon for cycloaddition under transition metal catalysis, which provides potential strategy for synthesizing other gem‐difluorinated carbocyclic molecules. [ABSTRACT FROM AUTHOR]