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 ΔGs 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.