Involvement of Triplet Excited States and Olefin Radical Cations in Electron-Transfer Cycloreversion of Four-Membered Ring Compounds Photosensitized by (Thia)pyrylium Salts

Miranda, Miguel A.; Izquierdo, and M. Angeles; Galindo, Francisco

doi:10.1021/jo011103i

Cited by 35 publications

(29 citation statements)

References 45 publications

(39 reference statements)

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“…[39] The oxetanes 1a and 1b were prepared by the PaternoϪBüchi photocycloaddition of benzaldehyde and trans-β-methylstyrene [33] or trans-anethole, [40] according to literature procedures. Characterization was achieved by 1 H and 13 C NMR spectra, which were recorded with a Varian Gemini 300 spectrometer at 300 MHz and 75 MHz, respectively. Data for the known compounds was consistent with that found in the literature.…”

Section: Methodsmentioning

confidence: 99%

“…[9] Control of the regioselectivity in the CR of oxetanes by photoinduced ET is synthetically interesting and constitutes the key step in the enzymatic repair of the (6Ϫ4) photoproducts of the DNA dipyrimidine sites by photolyase. [10Ϫ12] Prior to our work, [13,14] only two reports have appeared on the CR of oxetane radical cations. [3,4] They have proposed that the cycloreversion of 2-aryl-and 2,2-diaryloxetScheme 2 Electron-Transfer Cycloreversion of 2,3-Diaryloxetanes FULL PAPER anes using cyanoaromatic compounds as ET photosensitizers proceeds with initial C2ϪC3 bond breaking.…”

Section: Introductionmentioning

confidence: 99%

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Electron‐Transfer Cycloreversion of 2,3‐Diaryloxetanes: Influence of the Substitution and the Photosensitizer on the Regioselectivity

Izquierdo

Miranda

2004

Eur J Org Chem

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The regioselectivity in the oxidative electron-transfer cycloreversion (CR) of 2,3-diaryloxetanes depends on the substitution of the aryl groups and on the nature of the electrontransfer photosensitizer. The reaction occurs with fragmentation of the C2−C3 and C4−O bonds either in the presence of electron-releasing substituents in the 3-aryl groups, or when chloranil is used as photosensitizer. Thus, CR of the methoxysubstituted derivative trans,trans-3-(4-methoxyphenyl)-4-methyl-2-phenyloxetane (1b) results in the production of trans-anethole and benzaldehyde. In this case, the trans-ane-

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electron‐Transfer Cycloreversion of 2,3‐Diaryloxetanes: Influence of the Substitution and the Photosensitizer on the Regioselectivity

Izquierdo

Miranda

2004

Eur J Org Chem

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“…Since the triplet state 3 TTPP + * is accessed more efficiently than 3 TPT + *, this difference points to the importance of the triplet as the active excited state in the PET process, as explained in Scheme 5. 283 In laser flash photolysis experiments, either cyclobutane isomer 57.4 or 57.5 afforded only trans-stilbene (57.6) upon irradiation in the presence of TTPP-ClO 4 as the catalyst (eq 2). Thietanes can also undergo cycloreversion under similar reaction conditions.…”

Section: Triaryl Thiapyrylium: Photophysical and Electrochemical Charmentioning

confidence: 99%

Organic Photoredox Catalysis

2016

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In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

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“…On the other hand the cycloaddition of 1,3‐cyclohexadiene occurred with 95% conversion in one‐hour with less than 5% decomposition of the pyrylogen sensitizer. The formation of transient HPY + ˙ and stilbene radical cations were directly confirmed by UV–Visible spectroscopy and by laser flash photolysis in the 1,3‐cyclohexadiene cycloaddition and the cyclobutane cycloreversion reactions , respectively.…”

Section: Resultsmentioning

confidence: 87%

Synthesis, Characterization, Photophysics and Photochemistry of Pyrylogen Electron Transfer Sensitizers

Clennan

Liao

2013

Photochem & Photobiology

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A series of new dicationic sensitizers that are hybrids of pyrylium salts and viologens has been synthesized. The electrochemical and photophysical properties of these "pyrylogen" sensitizers are reported in sufficient detail to allow rationale design of new photoinduced electron transfer reactions. The range of their reduction potentials (+0.37-+0.05 V vs SCE) coupled with their range of singlet (48-63 kcal mol(-1)) and triplet (48-57 kcal mol(-1)) energies demonstrate that they are potent oxidizing agents in both their singlet and triplet excited states, thermodynamically capable of oxidizing substrates with oxidation potentials as high as 3.1 eV. The pyrylogens are synthesized in three steps from readily available starting materials in modest overall 11.4-22.3% yields. These sensitizers have the added advantages that: (1) their radical cations do not react on the CV timescale with oxygen bypassing the need to run reactions under nitrogen or argon and (2) have long wavelength absorptions between 413 and 523 nm well out of the range where competitive absorbance by most substrates would cause a problem. These new sensitizers do react with water requiring special precautions to operate in a dry reaction environment.

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Involvement of Triplet Excited States and Olefin Radical Cations in Electron-Transfer Cycloreversion of Four-Membered Ring Compounds Photosensitized by (Thia)pyrylium Salts

Cited by 35 publications

References 45 publications

Electron‐Transfer Cycloreversion of 2,3‐Diaryloxetanes: Influence of the Substitution and the Photosensitizer on the Regioselectivity

Electron‐Transfer Cycloreversion of 2,3‐Diaryloxetanes: Influence of the Substitution and the Photosensitizer on the Regioselectivity

Organic Photoredox Catalysis

Synthesis, Characterization, Photophysics and Photochemistry of Pyrylogen Electron Transfer Sensitizers

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