PHOTOCHEMICAL DIMERIZATION MODES OF 1-ACETYLANTHRACENE AND METHYL 1-ANTHRACENECARBOXYLATE

Irradiation of 1-acetylanthracene in dichloromethane at light waveleng ths above 400 nm gives five dimers in a ratio of about 2:1:1:1:1. In a ddition to the four typical modes of dimerization leading to symmetric al dianthracenes of anti-head-to-tail, syn-head-to-tail, anti-head-to- head and syn-head-to-head structures, 1-acetylanthracene undergoes dis symmetrical head-to-tail 4 pi + 4 pi cyclodimerization involving the 1 ,4 and 9',10' positions. Selective photoexcitation of 1-acetylanthrace ne in the presence of anthracene gives the mixed 9,10-9',10' and 1,4-9 ',10' 4 pi + 4 pi cycloadducts in a ratio of about 3:1. The photochemi cal dimerization of methyl 1-anthracenecarboxylate proceeds in the sam e fashion as that of 1-acetylanthracene.