Photoreduction of N-Methylphthalimide with 2,3-Dimethyl-2-butene. Evidence for Reaction through an Electron Transfer Generated Ion Pair

Article abstract of DOI:10.1021/ja00336a042

The photoreduction of N-methylphthalimide (NMP) in the presence of 2,3-dimethyl-2-butene (DMB) gives a pair of products (1 and 2) which could formally arise by hydrogen abstraction by the imide followed by coupling of the resultant radical pair at either of the two allylic positions on the 1,1,2-trimethylallyl radical.Sensitization and quenching studies have shown that these products arise from the singlet state of NMP and not triplet as previously suggested.Isotope effects studies with deuterium labeled DMB indicate that the reaction most probably proceeds by initial electron transfer to give the radical cation-radical anion pair.The ion pair either collapses to a zwitterionic precursor to 1 (13) or proton transfers to give a radical pair which subsequently collapses to 2.Isotope effect experiments indicate that decay of 13 to NMP and DMB is an efficient process relative to product formation.