Photochemical reaction of N-methylnaphthalene-1,8-dicarboximide with alkenes, dienes, and furans. Cyclobutane and oxetane formation

Abstract

Irradiation of benzene solutions of N-methylnaphthalene-1,8-dicarboximide (1) in the presence of alkenes (2b–k) and dienes (9a–c) give the cyclobutanes (3b–j), (4c,e,f,h,i), and (10a–c). Stereospecificity of cyclobutane formation was observed in the reaction with cis- and trans-but-2-ene (2h,i), and some endo-selectivity was observed in the reaction with styrene (2f). In contrast, irradiation of benzene solutions of (1) in the presence of trans- and cis-stilbene (2j,k), 2,5-dimethylbuta-2,4-diene (9d), and furans (14a,b) gave the fragmentation products (7a,b), (8), (13a,b), (16a,b), and (17a,b) arising via precursor oxetanes. In fluorescence quenching studies of the alkenes (2a–d) a linear relationship was found for log plots of their Stern-Volmer slopes (k_qτ) and ionization potentials, and the furans (14a) and (9d) showed new emissions, possibly from exciplexes. A tentative mechanistic scheme for the two types of reactions involving two types of exciplexes generated by the reaction of the singlet excited state of (1) and unsaturated compounds is proposed.