Visible‐Light Photocatalysis of the Ketyl Radical Coupling Reaction

Xia, Qing; Dong, Jianyang; Song, Hongjian; Wang, Qingmin

doi:10.1002/chem.201804873

Cited by 105 publications

(62 citation statements)

References 102 publications

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“…The reaction involved the concerted shift of a single electron and a single proton (proton‐coupled electron transfer (PCET) reactions [54] . Different photoredox reactions in which ketyl radical intermediates were formed through Brønsted acids activations were reported [55] . In the reaction performed with BIH, the absence of a Brønsted acid was probably responsible for the observed failures, as the redox potential of chlorobenzaldehyde was too negative for all the coumarins employed.…”

Section: Resultsmentioning

confidence: 99%

Tailored Coumarin Dyes for Photoredox Catalysis: Calculation, Synthesis, and Electronic Properties

et al. 2020

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High level time‐dependent density functional theory (TD‐DFT) computational modeling of coumarin dyes has been exploited for guiding the design of effective photocatalysts (PCs). A library of coumarins were investigated from the theoretical point of view and photophysical/electrochemical properties (absorption and emission spectra, E00, oxidation and reduction potentials) were evaluated. Comparison with literature values reported for a few candidates has been used for assessing the level of theory. On the basis of the results obtained, new strongly reducing PCs [Eox(PC.+/PC*)=−2.1 – −2.0 V vs SCE] were discovered. Through the computational study of structure‐properties relationships, a number of coumarins derivatives have been synthesized and evaluated in the pinacol coupling of aldehydes as the model reaction. The new organic photoredox catalysts show experimental photophysical and electrochemical data in accordance with the ones predicted by calculation, with excited state reduction potentials surpassing those of highly reducing transition metal‐based PCs. A careful investigation of their behavior as PC has revealed crucial issues that need to be taken into consideration in the general photoredox catalysis, shedding light on the use of these PC in the pinacol, as well as, in other photoredox reactions.

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Section: Resultsmentioning

confidence: 99%

Tailored Coumarin Dyes for Photoredox Catalysis: Calculation, Synthesis, and Electronic Properties

et al. 2020

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“…Usually, the SET process is promoted by alkaline or alkaline earth metals, transition metals, p-block elements and rare earth metals, 67 the photo-induced processes are not so common, possibly due to the poor selectivity achieved. 68 Graphitic carbon nitride (g-C3N4) 69 acted as semiconductor during the pinacol coupling catalyzed by simultaneous proton transfer from formic acid. The best conversion was obtained using 5 M NaOH-treated g-C3N4 in water being the pinacol adduct the major product obtained (61%) among others (Table 1, entry 1a) following the Type A mechanism (Scheme 30).…”

Section: Scheme 28 Semiconductor Cds As Promoter Of Photo-homocoupling Organic Processesmentioning

confidence: 99%

Photocatalytic Homocoupling Transformations

et al. 2021

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The homocoupling reactions promoted by photocatalysts are not very abundant in the literature but compounds generated from them are very interesting. In this short review the coverage of this item will be classified as follows on the basis of the starting material nature. 1. Introduction 2. Arenes and heteroarenes 3. Alkenes 4. Alkanes 5. Alkynes 6. Aldehydes, ketones, alcohols, amines and imines 7. Carboxylic acids 8. Nitrocompounds 9. Conclusions

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“…In sharp contrast to the radical anion of CO2, ketyl radical anions are considered as electron-rich species acting as single-electron reductants rather than forming C-C bonds via radical reactions. 81 When benzo[b]thiophene (3p, Scheme 8) was reacted with acetone (9a), the corresponding tertiary alcohol adduct 9pa was formed in good yield. The luminescence lifetime of TMAˉ* remains unchanged upon titration with acetone (−2.84 V vs. SCE in DMF) 82 and thus, the formation of a ketyl radical anion is unlikely ( Figure S11d, Supplemental Information).…”

Section: Mechanistic Insightsmentioning

confidence: 99%

Redox-neutral Photocatalytic C-H Carboxylation of Arenes and Styrenes with CO2

Schmalzbauer¹,

Svejstrup²,

Fricke³

et al. 2020

Preprint

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Carbon dioxide (CO2) is an attractive one-carbon (C1) building block in terms of sustainability and abundance. However, its low reactivity limits applications in organic synthesis as typically high-energy reagents are required to drive transformations. Here, we present a redox-neutral C−H carboxylation of arenes and styrenes using a photocatalytic approach. Upon blue-light excitation, the anthrolate anion photocatalyst is able to reduce many aromatic compounds to their corresponding radical anions, which react with CO2 to afford carboxylic acids. High-throughput screening and computational analysis suggest that a correct balance between electron affinity and nucleophilicity of substrates is essential. This novel methodology enables the carboxylation of numerous aromatic compounds, including many that are not tolerated in classical carboxylation chemistry. Over 50 examples of C−H functionalizations using CO2 or ketones illustrate a broad applicability. The method opens new opportunities for late-stage C−H carboxylation and valorization of common arenes.

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Visible‐Light Photocatalysis of the Ketyl Radical Coupling Reaction

Cited by 105 publications

References 102 publications

Tailored Coumarin Dyes for Photoredox Catalysis: Calculation, Synthesis, and Electronic Properties

Tailored Coumarin Dyes for Photoredox Catalysis: Calculation, Synthesis, and Electronic Properties

Photocatalytic Homocoupling Transformations

Redox-neutral Photocatalytic C-H Carboxylation of Arenes and Styrenes with CO2

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