Control of reaction pathways in the photochemical reaction of a quinone with tetramethylethylene by metal binding

Hiroaki Yamamoto, Kei Ohkubo, Seiji Akimoto, Shunichi Fukuzumi, Akihiko Tsuda

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The present study reports a novel supramolecular photochemical reaction that focuses on the direct electronic interactions between a host reaction substrate and guest metal salts. The reaction pathways in the photochemical reactions of quinone derivatives bearing a methoxy group and a long oligoether sidearm QEn (n = 0 and 3) with tetramethylethylene (TME) are changed upon noncovalent complexations of the host reactant with alkali and alkaline earth metal ions and a transition metal salt. The photochemical reaction of QEn with TME provides a mixture of [2 + 2] cycloadducts 1aE n and 1bEn, hydroquinone H2QEn, and monoallyl ether adducts of hydroquinones 2aEn and 2bEn. The photochemical reaction proceeds by the photoinduced electron transfer mechanism, where photoirradiation brings about formation of a radical ion pair [QEn-, TME+] as the primary intermediate. We found that the yields and selectivity of these photoproducts are changed upon electronic interactions of QEn- with the metal salts. The photochemical reaction in the absence of metal salts provides H 2QEn as its major product, whereas QE3, having the long sidearm, dominantly produces 2aE3 at the expense of 1aE 3, 1bE3, and H2QE3 when it forms a size-favorable host-guest complex with divalent Ca2+. In contrast, QEn selectively provides oxetanes 1aEn and 1bEn in the presence of Pd(OAc)2, which can form complexes with the quinone through metal-olefin and coordination interactions in the ground and photoexcited states of the quinone. This journal is

Original languageEnglish
Pages (from-to)7004-7017
Number of pages14
JournalOrganic and Biomolecular Chemistry
Issue number36
StatePublished - 28 Sep 2014


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