Convenient synthesis of 3-methoxybenz[a]anthracene-7,12-dione

The regioselective synthesis of 3-methoxybenz[a]anthracene-7,12-dione by oxidative photocyclization is described. The synthesis involved preparation of 1-(1-bromo-2-naphthyl)-2-(3- methoxyphenyl)ethylene by Wittig reaction, followed by photocyclization for 4 h. This gave 7-bromo-3-methoxybenz[a]anthracene. Extended photocyclization over 16 h under similar conditions gave 3-methoxybenz[a]anthracene-7,12-dione, an important intermediate in the synthesis of 7,12-dimethylbenz[a]anthracene-3,4-diol 1,2-epoxide.