Organic photochemistry. 77. Simultaneous capture of two distinct radical-ion intermediates generated from the EDA complexes of three-membered compounds with TCNE by photoexcitation and in the dark

Irradiation of the electron donor-acceptor (EDA) complexes of 2,2-diaryl-1-methylenecyclopropanes, 1,1,2,2-tetraarylcyclopropanes, 2,3-diaryloxiranes, or 2,3-diarylaziridines with tetracyanoethylene (TCNE) under aerated conditions involved oxygenation and/or the (3 + 2) cycloaddition with TCNE. The same oxygenation took place in the dark when the EDA complexes of 2,2-diaryl-1-methylenecyclopropanes or 1,1,2,2-tetraarylcyclopropanes with TCNE were simply stirred in oxygen-saturated solvents. Oxygenation occurred much more efficiently as the solvent polarity and the electron-donative nature of donor substrates increased. 1,2,4,5-Tetramethoxybenzene (TMB) used as a quencher efficiently suppressed oxygenation but not the (3 + 2) cycloaddition at all. Oxygenation occurs through the solvent-separated radical cations diffused from the photogenerated geminate radical ion pairs, whereas the cage coupling of the radical ion pairs involves the (3 + 2) cycloaddition with TCNE.