Photoinitiated Electron-Transfer Reactions of Aromatic Imides with Phenylcyclopropanes. Formation of Radical Ion Pair Cycloadducts. Mechanism of the Reaction

Article abstract of DOI:10.1021/jo00296a017

Few investigations have addressed the cyclization of a radical anion-radical cation pair resulting from photoinitiated electron transfer.One system that meets the criteria necessary to observe this phenomenon is the acceptor-donor pair N-methylphthalimide (NMP) and phenylcyclopropane (PC).Irradiation of NMP or N-methyl-2,3-naphthalimide (NMN) in the presence of PC in acetonitrile gave rise to two spiro tetrahydrofuranyl lactams.The regiochemistry and relative stereochemistry of these compounds were determined by NMR techniques and X-ray crystallography.The mechanism of the reaction proceeds via electron transfer from PC to the imide followed by coupling of the readical ion pair at the 1,2-position of the carbonyl to the cyclopropane ring in stepwise fashion.Fluorescence quenching experiments, reaction efficiency, and the free energy for electron transfer using various aromatic substituted phenylcyclopropanes provided strong evidence that electron transfer occurs.The reaction of cis-2-deutero-1-phenylcyclopropane (PC-d) with NMN established that the cycloaddition is stepwise rather than concerted and that both syn and anti reactive intermediates are equally accessible.