Continuous Flow Electrophotochemical Minisci Reaction via Catalytic Benzophenone Regeneration

Benzophenone is a widely used hydrogen atom transfer (HAT) photocatalyst, but its catalytic application is limited by ketyl radical dimerization to benzopinacol, which deactivates the catalytic cycle and stoichiometric loadings. In this work, we developed a continuous flow electrophotochemical strategy that enables in situ regeneration of benzophenone from benzopinacol. The process was implemented in a simple modular single-pass reactor that sequentially integrates photochemical activation and electrochemical turnover. Using this platform, Minisci-type C–H alkylation of pyridines was achieved under catalytic benzophenone conditions, affording the target product in up to 65% yield, whereas the yield dropped significantly in the absence of electrochemical recycling (Scheme 1). The method showed broad substrate scope and sustained activity during prolonged operation. This strategy was further extended to Giese-type addition and Paternò-Büchi cycloaddition, demonstrating its broader applicability to benzophenone-mediated photochemical reactions and converting an off-cycle deactivation pathway into a productive catalyst-regeneration manifold under continuous flow conditions.