Photooxygenation of 1,.omega.-Bis(diarylethenyl)alkanes via Photoinduced Electron-Transfer: Formation of 1,4-Radical Cations and Their Trapping by Molecular Dioxygen

Mizuno, Kazuhiko; Tamai, Toshiyuki; Hashida, Isao; Otsuji, Yoshio; Kuriyama, Yasunao; Tokumaru, Katsumi

doi:10.1021/jo00103a025

Cited by 36 publications

(18 citation statements)

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“…[16][17][18][19] Rate constants for radical cation mediated dimerizations of several other alkenes have been estimated by Stern-Volmer quenching and product studies [20][21][22] and by time-resolved methods. 23,24 The data previously measured for the radical cation mediated dimerization of styrenes demonstrate the effects of structure on the rate constants for the initial cycloaddition. However, the fact that both the structure of the radical cation and the alkene were changed at the same time made it difficult to draw firm conclusions about the relative importance of steric and electronic effects on the individual partners.…”

Section: Introductionmentioning

confidence: 75%

Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions¹

1996

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Absolute rate constants for the reactions of styrene, 4-methylstyrene, 4-methoxystyrene, and β-methyl-4-methoxystyrene radical cations with a series of alkenes, dienes, and enol ethers have been measured by laser flash photolysis. The measured rate constants correspond to either addition or electron transfer reactions, with the latter predominating when the oxidation potential of the alkene is lower than that of the styrene. The measured rate constants for the diene additions provide some of the first absolute kinetic data for the initial step in the syntheticallyuseful radical cation mediated Diels-Alder reaction. The addition reactions are sensitive to steric and electronic effects on both the radical cation and the alkene or diene. For example, the reactivity of the radical cations follows the general trend of 4-H > 4-CH 3 > 4-CH 3 O > 4-CH 3 O-β-CH 3 . The effects of alkyl substitution on the relative reactivity of alkenes toward styrene radical cations may be summarized as 1,2-dialkyl < 2-alkyl < trialkyl e 2,2dialkyl < tetraalkyl. The addition of the 4-methoxystyrene radical cation to a series of ring-substituted styrenes gives a reasonable Hammett correlation with a F value of -5. Thus, the addition of radical cations to a variety of alkenes and dienes follows similar trends to those observed for the addition of other electrophiles, such as diarylcarbenium ions. The results are consistent with previous suggestions of a concerted pathway for radical cation mediated cycloaddition reactions, although direct spectroscopic evidence for the initial product radical cation is obtained only for the additions to substituted styrenes.

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Section: Introductionmentioning

confidence: 75%

Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions¹

1996

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“…10 The mechanism is believed to involve photoinduced one-electron oxidation of the alkene to the corresponding radical cation (e.g., 1 to 1 •+ , Scheme 2). This reactive intermediate undergoes [2+2+2] cyclooxygenation with triplet oxygen to afford an endoperoxide radical cation ( 5 •+ ) that gives the 1,2-dioxolane product ( 5 ) upon reduction by either the reduced sensitizer or another equivalent of substrate.…”

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confidence: 99%

“…This reactive intermediate undergoes [2+2+2] cyclooxygenation with triplet oxygen to afford an endoperoxide radical cation ( 5 •+ ) that gives the 1,2-dioxolane product ( 5 ) upon reduction by either the reduced sensitizer or another equivalent of substrate. 10g The scope of the [2+2+2] cycloaddition, however, is quite limited when DCA is used as a photosensitizer, and only extremely electron rich 1,1-disubstituted styrenes (e.g., 1,1-bis( p -methoxyphenyl) ethylene) have been shown to give good yields of 1,2-dioxolane. This has been attributed to the ability of DCA to sensitize the formation of superoxide radical.…”

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confidence: 99%

“…This has been attributed to the ability of DCA to sensitize the formation of superoxide radical. 11 The formation of this reactive oxygen species is problematic because (1) superoxide reacts with alkene radical cations to produce oxidative cleavage products, 10b,12 which are the main products when less electron-rich olefins are utilized, and (2) competitive quenching of the photosensitizer by oxygen reduces the efficiency of the desired cyclooxygenation by decreasing the rate of formation of the key alkene radical cation.…”

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confidence: 99%

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Endoperoxide Synthesis by Photocatalytic Aerobic [2 + 2 + 2] Cycloadditions

Parrish

Ischay

et al. 2012

Org. Lett.

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Structurally novel endoperoxides can be sythesized by the photocatalytic cyclotrimerization of bis(styrene) substrates with molecular oxygen. The optimal catalyst for this process is Ru(bpz)32+, which is a markedly more efficient catalyst for these photooxygention reactions than conventional organic photosensitizers. The 1,2-dioxolane products are amenable to synthetic manipulation and can be easily processed to 1,4-diols and γ-hydroxyketones. An initial screen of the biological activity of these compounds reveals promising inhibition of cancer cell growth.

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“…[36][37][38][39] The alkene or diene precursors were commercially available (in the case of 1 a) or synthesized. In the final step of the syntheses, the endoperoxides precipitated out of solution and were purified by either recrystallization or column chromatography.…”

Section: Resultsmentioning

confidence: 99%

Efficient Homogeneous Radical‐Anion Chain Reactions Initiated by Dissociative Electron Transfer to 3,3,6,6‐Tetraaryl‐1,2‐dioxanes

Stringle

Magri²,

Workentin

2009

Chemistry A European J

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A series of 3,3,6,6-tetraaryl-1,2-dioxanes (TADs) have been investigated at an inert electrode by using cyclic voltammetry, constant potential electrolysis and digital simulations. The series consists of the phenyl-substituted TAD (1 a), p-methoxy-aryl TADs (1 b, 1 c) and the p-methoxy/nitro-bearing TAD (1 d). The heterogeneous electron-transfer (ET) reduction is dissociative, causing rupture of the oxygen-oxygen bond, which generates a distonic radical-anion that reacts competitively either by beta-scission fragmentation or ET. Fragmentation of the distonic radical anion yields an alkene, a substituted benzophenone, and a benzophenone radical anion. The benzophenone radical-anion propagates an efficient homogeneous ET-fragmentation chain reaction that accounts for the potential dependence of the product ratios and the low charge consumption observed in the controlled potential electrolysis experiments. Digital simulation of the experimental cyclic voltammograms allowed for estimates of the rate constants of the heterogeneous ET to the O--O bond, and for the rate constants for the beta-scission fragmentation of the distonic radical-anions. Density functional theory calculations corroborate the differences in the heterogeneous kinetics of the initial dissociative ET. The endoperoxides 1 a-1 c react predominantly by a concerted dissociative ET mechanism, although the data suggests a stepwise dissociative pathway is also competitive. Bearing a nitro-aryl substituent, 1 d provides a rare example of an endoperoxide that proceeds by a stepwise dissociative ET mechanism. Irrespective of the initial mechanistic details, we find a propagating radical-anion cycle is a general mechanistic feature.

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Photooxygenation of 1,.omega.-Bis(diarylethenyl)alkanes via Photoinduced Electron-Transfer: Formation of 1,4-Radical Cations and Their Trapping by Molecular Dioxygen

Cited by 36 publications

References 0 publications

Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions¹

Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions¹

Endoperoxide Synthesis by Photocatalytic Aerobic [2 + 2 + 2] Cycloadditions

Efficient Homogeneous Radical‐Anion Chain Reactions Initiated by Dissociative Electron Transfer to 3,3,6,6‐Tetraaryl‐1,2‐dioxanes

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Photooxygenation of 1,.omega.-Bis(diarylethenyl)alkanes via Photoinduced Electron-Transfer: Formation of 1,4-Radical Cations and Their Trapping by Molecular Dioxygen

Cited by 36 publications

References 0 publications

Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions1

Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions1

Endoperoxide Synthesis by Photocatalytic Aerobic [2 + 2 + 2] Cycloadditions

Efficient Homogeneous Radical‐Anion Chain Reactions Initiated by Dissociative Electron Transfer to 3,3,6,6‐Tetraaryl‐1,2‐dioxanes

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Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions¹

Reactivity of Radical Cations. Effect of Radical Cation and Alkene Structure on the Absolute Rate Constants of Radical Cation Mediated Cycloaddition Reactions¹