Reinvestigation in the photoreaction of 1-naphthalenecarbonitrile and furan

Photocycloaddition of furan to 1-naphthalenecarbonitrile (1) was reinvestigated. Irradiation of the mixture through Pyrex filter yielded endo-4+4] adduct (2) and syn-2+2] adduct (4). Considering the secondary orbital interaction in the singlet-state 4+4] photocycloaddition, the favorable formation of exo-4+4] cyclodimer (3) over 2 followed by a facile Cope rearrangement was proposed for the formation of 4, and confirmed by a low temperature irradiation experiment.