Aerobic Direct C(sp2)‑H Hydroxylation of 2‑Arylpyridines by Palladium Catalysis Induced with Aldehyde Auto-Oxidation

Herein we present a Pd-catalyzed direct C–H hydroxylation of 2-arylpyridines using molecular oxygen (O₂) as the sole oxidant. The key aspects of the method include: (a) the activation of molecular oxygen with a nontoxic and inexpensive aldehyde; (b) an efficient association of the in situ-generated acyl peroxo radical with palladium catalysis; and (c) convenient operating conditions. On the basis of the results obtained in a series of control experiments, a Pd^II/Pd^IV catalytic cycle is implicated for the transformations. Furthermore, the method offers an easy access to a broad range of substituted 2-(pyridin-2-yl)­phenols in good isolated yields.