A [3+2]-Photocycloaddition of 9,10-Dicyanophenanthrene to 1,3-Butadiene

In the photoreactions of 9,10-dicyanophenanthrene (6) with 1,3-butadiene (7) a novel [3+2]-photocycloaddition at the 9,10position of the phenanthrene ring of 6 to one of the double bond of 7 and a [2+2]-cycloaddition at the 9,10-position of 6 were found to proceed from the singlet and the triplet excited states of 6, respectively