Efficient Co(OAc)2-catalyzed aerobic oxidation of EWG-substituted 4-cresols to access 4-hydroxybenzaldehydes

We reported an efficient ligand-free Co(OAc)2·4H2O/NaOH/O2/ethylene glycol reaction system that enables selective aerobic oxidation of a wide range of substrates covering 2,6-di-EWG-, 2,3,6-tri-EWG-, 2-EWG-, and 2-EWG-6-EDG-substituted 4-cresols into the corresponding 4-hydroxybenzaldehydes. Based on the experimental investigations and well-defined p-benzoquinone methides, a plausible reaction mechanism was proposed. Considering the simplicity of the procedure and importance of the products, the methodology was expected to become a favorable and practical tool in related benzylic C(sp3)-H functionalization chemistry.