Tungstate-Catalyzed Selective Oxidation of Naphthalenols to Afford Diverse Products under Mild Conditions

Selective oxidations of naphthalenols and naphthaleneylboronic acids/esters have been achieved under mild conditions utilizing tungstate/H₂O₂ at room temperature. Diverse products were obtained in moderate to excellent yields by slightly adjusting the reaction conditions, including 2-carboxycinnamic acid, 1,2-naphthoquinone (1,2-NQ), naphthalenol-1,2-NQ dimers, and <i>o</i>-hydroxyl-NQ. Notably, some 2-carboxycinnamic acid and 1,2-NQ derivatives could be isolated via filtration without column chromatography purification. Using this method, the total synthesis of daldiquinone was accomplished in two steps. Based on mechanistic studies, the phenolic hydroxyl group acted as a directing group to control the <i>ortho</i>-selective oxidation, and the <i>o</i>-hydroxyl-NQ could also undergo Bayer-Villiger oxidation to generate an anhydride intermediate.