Flow‐Enabled Direct Photochemical Functionalization of Aryl Fluorides

Direct functionalization of aryl fluorides remains challenging because of the exceptional strength of the C-F bond and the reliance of existing methods on tailored catalysts or activated substrates. Here, we report a catalyst-free photochemical strategy for the direct functionalization of electron-rich fluoroarenes using UV irradiation in flow. A simple 3D-printed microfluidic reactor paired with a commercially available UV source enables C-F activation under operationally simple conditions, without the need for redox matching or external catalysts. The method accommodates a broad range of electron-rich arenes and heteroarenes for C-C bond formation and can be extended to C-P bond formation using triethyl phosphite as a nucleophilic coupling partner. The continuous-flow platform also enables direct scale-up without re-optimization. Mechanistic studies, including isotope-labeling experiments, radical trapping studies, intramolecular cyclization probes, EPR spectroscopy, and DFT calculations, support a complex reaction manifold involving contributions from both heterolytic and homolytic C-F cleavage pathways. This work establishes direct UV activation in flow as a simple and scalable platform for aryl fluoride diversification.