Gem-Difluorocyclopropenes as Versatile β-Monofluorinated Three-sp2 Carbon Sources for Cp*Rh(III)-Catalyzed [4+3] Annulation: Experimental Development and Mechanistic Insight

Cp*Rh(III)-catalyzed [4 + 3] annulation of N-methoxy amides for the direct assembly of seven-numbered 2H-azepin-2-one frameworks has been realized with gem-difluorocyclopropenes acting as innovative beta-monofluorinated three sp(2) carbon sources. Either annular arylamides or linear acrylamides with the embedment of various functional groups, including DNA-tagged substrates, were found to be compatible with the established [4 + 3] reaction mode. A redox-neutral Rh(III)-Rh(V)-Rh(III) catalytic cycle, specifically via HOAc-assisted tandem site-/regioselective oxidative addition/reductive elimination/C-F bond cleavage-enabled ring-scission involving the unprecedented olefinic C(sp(2))-C(sp(2)) bond cleavage, has been deduced based on experimental and computational mechanistic studies. Taken together, our findings not only identified gem-difluorocyclopropenes as potent and efficient coupling partners for C-H activation development but also provided a sound basis for the organic integration of transition-metal-catalyzed C-H functionalization with cyclopropene and fluorine chemistries.