The Photoreactions of 2,3-Dicyanobarrelene

Abstract
The direct irradiation of 2,3-dicyanobarrelene (II) provided 1,2-dicyanocyclooctatetraene (III). On the other hand, the acetone-sensitized photoreaction of II afforded semibullvalene derivatives (IV and V). Investigations of their NMR spectra clarified that IV completely degenerates, whereas V inclines to the favorable form of the valence isomers.