The Addition of Alcohol to 1,2-Naphthoquinone Promoted by Metal Ions. A Facile Synthesis of 4-Alkoxy-1,2-naphthoquinones

Abstract

Abstract In the presence of some metal ions and sodium iodate, 1,2-naphthoquinone (1) readily reacted with methanol to give 4-methoxy- 1,2-naphthoquinone (2a). The activity of the metal ions increased in the following order: Co(II)<Ni(II) << Cu(II)<La(III) << Ce(III). The reaction was remarkably affected by the reaction temperature, reaction time, and molar ratio of the chelating agent. By the use of 1 equivalent of cerium salt to 1, the yield of 2a increased to 81% at 20 °C for 30 min. In higher alcohols, the addition reaction proceeded under similar conditions to give 4-alkoxy-1,2-naphthoquinones (2b–f) in 46–75% yields.