Rhodium‐Catalyzed 1,5‐Sigma Migratory Ring Expansion of <i>gem</i> ‐Difluorodienyl Cyclopropanes and Cyclobutanes

Abstract

Abstract Rhodium‐catalyzed 1,5‐sigma migratory ring expansion (SMRE) of common dieneylcyclopropanes (DECPs) and dieneylcyclobutanes (DECBs) fails. But replacing the terminal CH 2 group with CF 2 group for both DECPs and DECBs, the resulting substrates of gem ‐difluorodienyl cyclopropanes (df‐DECPs) and gem ‐difluorodienyl cyclobutanes (df‐DECBs) can achieve this reaction, which has broad reaction scope and high efficiency to give seven‐ and eight‐membered carbocycles with a carbonyl group. The keys to the success of this reaction are: oxidative cyclometalation becomes easier with the help of two F atoms; the metallacycle intermediate can detour the sluggish reductive elimination by defluorination to generate Rh carbene intermediate (defluorocarbenation process), which can undergo easier carbene migratory insertion and β‐H elimination, giving rise to the final products. Mechanistic studies via experiments and quantum chemical calculations support the proposed mechanism. The gem ‐difluoro ene in the substrates of df‐DECPs and df‐DECBs of the present SMRE reaction can be regarded as a ketene surrogate, and this strategy can be exploited in many transition‐metal‐catalyzed reactions in the future.