Competitive Photochemical ?2 + ?2 Addition and Electron Transfer in the N-Methylphthalimide-Alkene System

Article abstract of DOI:10.1021/jo00215a017

N-Methylphthalimide (NMP) undergoes a pair of competing photochemical reactions in the presence of alkenes.In one of these reactions the alkene adds to the C(O)-N bond of NMP in a concerted ?² + ?² process that ultimately leads to 2-benzazepine-1,5-diones (5).A competing electron-transfer process results in the formation of a radical cation-radical anion pair which can be efficiently trapped in alcohols solvents such as 4.The regiochemistry of these products is consistent with expectations for addition of an alcohol to a radical cation.Calculations usingthe Weller equation accurately predict when electron transfer should dominate the ?² + ?² process, when the ?² + ?² process should dominate the electron transfer process, and when the two should be directly competitive.Product studies on the formation of 4 and 5 for various alkenes in methanol solution are entirely consistent with this hypothesis.