Triphenylpyrylium salt-sensitized photoreactions of 1,4-diaryl-2,3-dioxabicyclo[2.2.2]octanes through competitive single electron-transfer pathway and proton-catalyzed pathway |
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| Authors: | Masaki Kamata Jun-ichi Kaneko Ryoichi Akaba |
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| Institution: | a Department of Chemistry, Faculty of Education and Human Science, Niigata University, Ikarashi, Niigata 950-2181, Japan
b Department of Chemistry and Advanced Engineering Courses, Gunma College of Technology, 580 Toriba-machi, Maebashi, Gunma 371-8530, Japan |
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| Abstract: | 2,4,6-Triphenylpyrylium tetrafluoroborate (TPPBF4)-sensitized photoinduced electron-transfer (PET) reactions of 1,4-diaryl-2,3-dioxabicyclo2.2.2]octanes 5 (a: Ar1 = Ar2 = p-MeOC6H4, b: Ar1 = Ar2 = p-MeC6H4, c: Ar1 = Ar2 = Ph) underwent novel fragmentation through their radical cations to give 1,4-diarylbutan-1,4-diones 6 accompanied by elimination of ethylene. On the other hand, 4-aryl-cyclohex-3-en-1-ones 7, p-substituted phenols 8, and 4-aryl-4-aryloxycyclohexanones 9 were produced through proton-catalyzed pathways when the PET reactions of 5 were performed in the absence of a certain base such as 2,6-di-tert-butylpyridine (DTBP). Particularly, the formation of 9 is consistent with the novel cationic rearrangement involving nucleophilic O-1,2-aryl shifts and C-1,4-aryl shifts. |
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| Keywords: | Triphenylpyrylium tetrafluoroborate 1 4-Diaryl-2 3-dioxabicyclo[2 2 2]octane Photoinduced electron-transfer Single electron-transfer Radical cation Proton-catalyzed reaction O-1 2-Aryl shift C-1 4-Aryl shift |
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