Photochemical Reactions of N-Methylnaphthalene-2,3-dicarboximide with Alkenes

Article abstract of DOI:10.1021/jo00373a012

Previous studies have been shown that N-methylphthalimide (NMP) reacts with alkenes to afford, in a few cases, oxetanes, along with products of alkene addition to the C(O)N bond and products arising from initial electron transfer.In this paper we explore the photochemistry of N-methylnaphthalene-2,3-dicarboximide (NMN).The photochemistry of NMN was studied in benzene, a solvent which we were unable to use with NMP due to solubility factors.In this solvent oxetanes were the major products found with several alkenes (α-methylstyrene, diphenylethylene, styrene, trans-stilbene).In the case of trans-stilbene a novel 2 + 2 addition to the 1,2-bond of NMN was also observed to give a photochemically labile cyclobutane.In benzene solvent alkene addition to the C(O)N bond was never a major product.Also investigated was a series of alkenes in acetonitrile containing methanol in which the expected products obtained by trapping the electron-transfer-generated radical anion radical cation pair with methanol were found.In the case of 2,3-dimethyl-2-butene there was observed a pair of photoreduction products analogous to those observed with this alkene and NMP.A study of solvent polarity effects on the ratio of these photoreduction products supports the previous suggestion that one of these arises via proton transfer followed by coupling of the radical pair, whereas the other comes from a rare case of radical cation-radical anion coupling followed by intramolecular proton transfer in the resultant zwitterion.Fluorescence quenching data for NMN with a series of unsaturated hydrocarbons are presented, and these data are shown to correlate well with the Weller equation.