The 2- or 6-(α-Hydroxyalkyl- and α-Oxoalkyl)-5,8-dimethoxy-1,4-naphthoquinones from the Oxidative Demethylation of 2-(α-Hydroxyalkyl- and α-Oxoalkyl)-1,4,5,8-tetramethoxynaphthalenes with Cerium(IV) Ammonium Nitrate, and the Further Demethylations to Naphthazarins

Abstract

Oxidative demethylation of 2-(α-hydroxyalkyl- and α-oxoalkyl)-1,4,5,8-tetramethoxynaphthalene with (NH4)2Ce(NO3)6 gave two isomeric dimethoxynaphthoquinones: 2-substituted and 6-substituted 5,8-dimethoxy-1,4-naphthoquinones. Further demethylations of the former isomers to the corresponding dihydroxynaphthoquinones required an AgO–40%HNO3 reagent, while the latter isomers needed AlCl3 as the demethylation reagent. Some comments regarding the mechanism of these oxidative demethylations with (NH4)2Ce(NO3)6 are given.