Regioselective oxidation of 1,4-dialkoxy-5,8-dimethoxynaphthalenes with ammonium cerium(IV) nitrate

Oxidation of 1,4-dialkoxy-5,8-dimethoxynaphthalenes (1) with ammonium cerium (N) nitrate (CAN) gave two regioisomeric quinones whose ratio was affected by an electronic difference between methoxy and alkoxy groups. Substrates having electron-donating alkoxy groups as compared with methoxy ones gave mainly 5,8-dimethoxy-1,4-naphthoquinone (3); the minor was 5,8-dialkoxy-1,4-naphthoquinone (2). On the other hand, substrates bearing electron-withdrawing groups preferentially afforded 2. Oxidation of 1,4-diacetoxy-5,8-dimethoxynaphthalene (li) with CAN gave only 5,8-diacetoxy-1,4-naphthoquinone (2i).