Synthesis of naphthoquinones utilizing cobalt-salen catalyst

Abstract

Under mild condition, utilizing cobalt-salen catalyst with oxygen, 1-naphthol could be oxidized to the corresponding 1,4-naphthoquinone product at room temperature in good yield. The optimum reaction conditions studied including reaction time, type of oxidant, type and amount of ligand, temperature and type of solvent were explored. The oxygenation of 2-naphthol under the developed oxidation process could yield a dimeric compound, namely 4-(2-hydroxy-1-naphthyl)-1,2-naphthoquinone in satisfactory. In addition, this developed condition was applied to the oxidation of thymol, 1,5-dihydroxynaphthalene, 6-methoxy-2-naphthol, 7-methoxy-2-naphthol into the corresponding thymoquinone, juglone, 6-methoxy-1,2-naphthoquinone and 4-(2-hydroxy-7-methoxy-1-naphthyl)-7-methoxy-1,2-naphtho-quinone in moderate yield