Green Light-Driven Hydroxylation of Boronic Acids Employing g-C₃N₄ as the Photocatalyst

Phenol derivatives display a prominent role in many biologically active molecules. Boron-containing molecules are considered valuable precursors for their synthesis. Therefore, the rise of photochemistry has led many researchers to develop novel, sustainable protocols that exploit the advantages offered by different irradiation sources. For this reason, the application of novel photocatalysts that promote challenging organic transformations is highly valued. Graphitic carbon nitride (g-C₃N₄) is a semiconductor photocatalyst widely used in organic chemistry for promoting complex organic transformations. Herein, we report a green and efficient methodology for the hydroxylation of boronic acids to the corresponding hydroxyl derivatives, using g-C₃N₄ as the photocatalyst. The heterogeneous photocatalyst (g-C₃N₄) was prepared by thermal polycondensation of melamine and characterized by XRD, FESEM/EDS, and UV-Vis diffuse reflectance spectroscopy. Green LED irradiation was employed as the energy source and air as the active oxidant. A variety of substrates were tested, showcasing excellent functional group tolerance in the aerobic photochemical protocol. Mechanistic studies were conducted to investigate the reaction pathway and to identify the oxygen species generated.