The photochemical reactions of a variety of vinylbenzo-1,4-quinones have be
en investigated. Irradiation of a benzene solution of 2-methyl-5-(1-phenylv
inyl)benzo-1,4-quinone affords quantitatively a benzofuranol via intramolec
ular cyclization, while the styryl derivative gives a novel dimer by way of
intermolecular (4 + 2) cycloaddition. In contrast to these two quinones, t
he (2,2-diphenylvinyl) derivative gives a phenanthrene-1,4-quinone via a st
ilbene-like photocyclization, The reaction paths of these intra- and interm
olecular photochemical reactions are also discussed.