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.

Electron-Transfer-Induced Intermolecular [2 + 2] Cycloaddition ReactionsBased on the Aromatic "Redox Tag" Strategy. -Aliphatic cyclic enol ethers undergo novel electron-transfer-induced [2 + 2] cycloaddition with unactivated olefins possessing aromatic "redox tag". The latter also facilitates electron-transfer-induced cycloreversion of cyclobutanes. In contrast to alkoxyphenyl and alkylphenyl groups, aminophenyl and thiophenol units cannot function as aromatic "redox tag". -(OKADA, Y.; NISHIMOTO, A.; AKABA, R.; CHIBA*, K.; J. Org. Chem. 76 (2011) 9, 3470-3476, http://dx.