Electronically controlled regioselective hydroarylation of gem-difluoroallenes

All-carbon quaternary centers are ubiquitous structural motifs in natural products, bioactive molecules, and pharmaceuticals. The formation of these crowded carbon centers is well known to be challenging, and methods to access them remain in high demand. Transition-metal-based strategies have emerged as a powerful approach to quaternary carbons, primarily relying on cross-coupling reactions and olefin arylation processes. Herein is presented a straightforward method to create benzylic all-carbon quaternary centers employing gem-difluoroallenes. Features of this method include room temperature C–H functionalization, excellent regioselectivity in the insertion of gem-difluoroallenes, and generation of gem-difluoroalkene products, which have widespread applications in synthesis and pharmaceutical sciences. Mechanistic studies support a turnover limiting rhodium-catalyzed C–H cleavage that likely proceeds via a concerted metalation deprotonation pathway. Regioselective insertion of the gem-difluoroallene is controlled by electronic effects.