Intramolecular Photocycloaddition Reactions of Arylcyclopropane Tethered 1‑Cyanonaphthalenes

Intramolecular photocycloaddition
reactions of 1-cyanonaphthalenes
bearing an arylcyclopropane containing side chain were investigated.
Photoreactions of members of this family in which the arylcyclopropane
moiety is bonded at the 2-position of the 1-cyanonaphthalene ring
produce head-to-head and head-to-tail 1,2-[3+2] photocycloadducts.
On the other hand, substances in this family containing an arylcyclopropane
side chain linked to the 4-position of the cyanoarene ring undergo
photoreactions to form [4+3] photocycloadducts along with novel nine-membered
ring products, which are produced by photochemically induced 10π
conrotatory ring opening of the initially formed intramolecular [3+2]
cycloadducts. The results of solvent effects and fluorescence investigations
along with those focusing on corresponding intermolecular photoreactions
demonstrate that the photocycloadducts are formed predominantly through
an intramolecular exciplex mechanism and that a photoinduced intramolecular
electron transfer pathway via zwitterionic biradicals might be partly
responsible for the process when CH3CN is the solvent.