Intramolecular acetalisation of naphthoquinones

Abstract

Attempts have been made to synthesise the glyceride quinone 2-cyclohexyl-3-(1,2-dihydroxyethyl)methoxy-1,4-naphthoquinone (3) as a prodrug of 2-cyclohexyl-3-hydroxy-1,4-naphthoquinone (4). The intermediate 2-cyclohexyl-3-(2,2-dimethyl-1,3-dioxolan-4-yl methoxy)-1,4-naphthoquinone (6), required for the projected synthesis, was readily obtained. However, on acid treatment this compound unexpectedly furnished 5-cyclohexyl-10b,2-epoxymethano-(7) and 5-cyclohexyl-10b,3-epoxymethano-2,3-dihydronaphtho[1,2-b]dioxin-6(10bH)one (8). The structures of these compounds have been established by spectroscopic and degradative studies and a mechanism is proposed to account for their formation.