Triphenylpyrylium tetrafluoroborate (TPP ' BF,) has been found to sensitize oxygenation of adamantylideneadamantane to its dioxetane in good yield. Product studies, measurements of quantum yields for dioxetane formation, laser flash photolysis, and quenching experiments of TPP' fluorescence by various electron donors have been carried out to elucidate the mechanism for dioxetane formation. Cyclic voltammetry was also used to examine the reactivity of pyryl radicals (TPP') with molecular oxygen. The results are consistent with a mechanism involving electron transfer from the alkene to the excited states of TPP' to give radical pairs consisting of the alkene radical cations and TPP'. The alkene radical cation reacts with molecular oxygen to afford the dioxetane. A singlet oxygen mechanism is not likely since the quenching rate of the excited triplet state of TPP' by the alkene is 400 times faster than by dissolved oxygen under the p hotooxyg en at ion c o nd it i o ns.

Novel electron-transfer-induced intermolecular [2+2] cycloaddition reactions between an aliphatic cyclic enol ether and several unactivated olefins have been demonstrated on the basis of the aromatic "redox tag" strategy. The aromatic "redox tag" was oxidized during the formation of the cyclobutane ring, affording the relatively long-lived aromatic radical cation, which was then reduced to complete the overall reaction that constructed the corresponding [2+2] cycloadducts. The aromatic "redox tag" was also found to facilitate electron-transfer-induced cycloreversion reactions of cyclobutane rings.

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The electronic structures and molecular conformations of N-benzylideneaniline and its several derivatives bearing 2-methyl, 2,6-dimethyl, and/or 4-nitro groups on the anilino benzene ring (ring A) have been investigated by electronic absorption spectroscopy combined with CNDO/S CI calculations. The lower energy bands are assigned and the molecular conformations are estimated. The results show that the 4-nitro derivatives as well as the 2,6-dimethyl derivatives take considerably twisted conformations.

Electrocatalytic formal [2+2] cycloadditions between anodically activated aliphatic enol ethers and unactivated olefins possessing an alkoxyphenyl group have been accomplished in a lithium perchlorate/nitromethane electrolyte solution. The alkoxyphenyl group was revealed to play an important role in the reaction intermediates to complete formation of the cyclobutane ring through intramolecular electron transfer between the cyclobutane radical cation and the alkoxyphenyl group.