1,3-Dipolar character of six-membered aromatic rings. Part XXVII. Photochemically induced valence bond tautomerism and dimerisation of 3-oxido-1-phenylpyridinium

Abstract

Irradiation of the title compound (1) yields one of the photochemically allowed symmetrical dimers (16) together with a bicyclic valence bond isomer (7) and two stereoisomers (18) and (20) of thermal addition products of (7) to a second molecule of the starting phenyl betaine. Analogues (19) and (21) of the dimers (18) and (20) were prepared by reaction of isolated (7) with the pyrimidine betaine (2). Irradiation of (1) in allyl alcohol affords an addition product (24) of (7).