-- Note --

Regioselective Oxidation of 1,4-Dialkoxy-5,8-dimethoxynaphthalenes
with Ammonium Cerium (IV) Nitrate

Yasuhiro TANOUE*, Kazunori SAKATA†, Mamoru HASHIMOTO†, Shin-ichi MORISHITA††,
Moritugu HAMADA, Norihisa KAI and Takeshi NAGAI

Department of Food Science and Technology, National Fisheries University;
Nagatahonmachi, Shimonoseki-shi 759-6595 Japan
† Department of Chemistry, Faculty of Engineering, Kyushu Institute of Technology;
Tobata-ku, Kitakyushu-shi 804-8550 Japan
†† Department of Marine Engineering, National Fisheries University; Nagatahonmachi,
Shimonoseki-shi 759-6595 Japan

Oxidation of 1,4-dialkoxy-5,8-dimethoxynaphthalenes (1) with ammonium cerium (IV) 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 (1i) with CAN gave only 5,8-diacetoxy-1,4-naphthoquinone (2i).


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