Intramolecular Photoreactions of 9-Cyanophenanthrene-Linked Arylcyclopropanes

With the aim of developing efficient and useful processes for the preparation of polycyclic organic compounds, intramolecular [3 + 2] photoreactions of 9-cyanophenanthrene-linked arylcyclopropanes were investigated. Photoreactions of 6a,b , which contain respective p -methoxyphenylcyclopropane and phenylcyclopropane moieties, form the intramolecular [3 + 2] photocycloadducts, endo- and exo- 7a,b , along with the dihydroisochroman derivatives, cis- and trans- 8a,b . The efficiency of the photoreaction of 6a is higher when benzene rather than acetonitrile is used as a solvent. Interestingly, this solvent effect is reversed in the photoreaction of 6b , where the efficiency is higher in acetonitrile than that in benzene. On the basis of the observed effects of substituents and solvents, fluorescence emission from intramolecular exciplexes, and Δ G s for intramolecular single electron transfer (SET), we propose that the photoreactions proceed through pathways involving the initial formation of singlet intramolecular exciplexes and/or SET between the excited 9-cyanophenanthrene and the ground-state arylcyclopropane moieties.