1,8-Diacetylnaphthalene and its cyclisation to 3-methyl-1H-phenalen-1-one

Abstract

A single isomer of 1,8-diacetylnaphthalene (I) was formed on oxidation of cis- or trans-1,2-dimethylacenaphthene-1,2-diols (II). The dipole moment of diketone (I)(2.37 D) corresponds precisely to that calculated (CNDO/2) for the trans-isomer. Cyclisation of (I) to 3-methyl-1H-phenalen-1-one was achieved in 45 : 55 (v/v) ethanol–water solution on acid or alkali catalysis, or on electrochemical reduction. The rates of these reactions were measured, the cyclisation with alkali proceeding at ca. 50 000 times the rate of the reaction with acid. An explanation for the cyclisation on electrochemical reduction was obtained from calculations (INDO) of electron-densities of the radical anion of (I).