Photocycloaddition of 4-dimethylaminostyrene with 1-vinylpyrene or styrene

Abstract

Photocycloaddition reactions of 4-dimethylaminostyrene (1) as an electron donor with 1-vinylpyrene (2) or styrene (3) as electron acceptors were studied. In non-polar solvents, photoirradiation of (1) with (2) gave trans- and cis-1-(4-dimethylaminophenyl)-2-pyren-1-ylcyclobutane (4t and 4c), whereas photoreaction of (1) with (3) gave only cis-1-(4-dimethylaminophenyl)-2-phenylcyclobutane (5). The yield of these cycloadducts decreased with increasing solvent polarity, and in polar solvents mainly the copolymer was produced. Transient intermediates were studied by nanosecond ruby laser photolysis of the system (1)+(2). The transient absorption spectrum in the non-polar solvent benzene was ascribed to the exciplex type, while in the polar solvent acetonitrile the spectrum of free cation and anion radicals was observed. These facts imply that photochemical cycloaddition of these systems occurred via an exciplex as the intermediate. The formation of cis- and trans-cycloadducts is discussed in terms of the reactivity of the exciplex state and the conformation of the exciplex.