Intra- and intermolecular photocyclization of vinylbenzo-1,4-quinones

The photochemical reactions of a variety of vinylbenzo-1,4-quinones have been investigated. Irradiation of a benzene solution of 2-methyl-5-(1-phenylvinyl)benzo-1,4-quinone affords quantitatively a benzofuranol via intramolecular cyclization, while the styryl derivative gives a novel dimer by way of intermolecular (4 + 2) cycloaddition. In contrast to these two quinones, the (2,2-diphenylvinyl) derivative gives a phenanthrene-1,4-quinone via a stilbene-like photocyclization. The reaction paths of these intra- and intermolecular photochemical reactions are also discussed.