Photochemical C–H acetalization of O-heterocycles utilizing phenylglyoxylic acid as the photoinitiator

Koutoulogenis, Giorgos S.; Spiliopoulou, Nikoleta; Kokotos, Christoforos G.

doi:10.1007/s43630-021-00126-7

Cited by 10 publications

(7 citation statements)

References 51 publications

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“…The low quantum yield in the acid release (<0.05, Table ) did not hamper the synthetic applications of the examined PAGs, as demonstrated by the protection of alcohols as THP ethers. The formation of these ethers starting from 3,4-dihydro-2 H -pyran (DHP) is commonly used to protect hydroxyl functional groups. , This reaction may be carried out by using a plethora of protocols , but some drawbacks still remain. Thus, the acid catalysts mostly used may induce the formation of polymeric byproducts derived from DHP or may be incompatible with other acid-sensitive functional groups.…”

Section: Discussionmentioning

confidence: 99%

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

et al. 2022

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The selective visible-light-driven generation of a weak acid (sulfinic acid, in nitrogen-purged solutions) or a strong acid (sulfonic acid, in oxygen-purged solutions) by using shelf-stable arylazo sulfones was developed. These sulfones were then used for the green, smooth, and efficient photochemical catalytic protection of several (substituted) alcohols (and phenols) as tetrahydropyranyl ethers or acetals.

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Section: Discussionmentioning

confidence: 99%

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

et al. 2022

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“…On the other hand, the α‐oxyalkyl radical ( 2 a⋅ ) can be trapped by minor amounts of solubilized Cl 2 ‐formed via the anodic oxidation of chloride‐resulting in a chloride intermediate ( 2 a‐Cl ) [23a] . Although the intermediate 2 a‐Cl was not observed in our experiments, it would theoretically lead to the formation of product 3 via nucleophilic substitution, aided by the anomeric effect [24] . Despite extensive efforts, the C(sp 3 )−H heteroarylation method could not be extended to unactivated aliphatic C(sp 3 )−H bonds (see Supporting Information).…”

Section: Methodsmentioning

confidence: 70%

“…[23a] Although the intermediate 2 a-Cl was not observed in our experiments, it would theoretically lead to the formation of product 3 via nucleophilic substitution, aided by the anomeric effect. [24] Despite extensive efforts, the C(sp 3 )À H heteroarylation method could not be extended to unactivated aliphatic C(sp 3 )À H bonds (see Supporting Information). The fact that these substrates are unreactive suggests that the oxidation from intermediate 2 a * to 2 a + is only realized when the latter is adequately stabilized, as observed with an oxocarbenium ion.…”

Section: Methodsmentioning

confidence: 99%

Accelerated Electrophotocatalytic C(sp³)−H Heteroarylation Enabled by an Efficient Continuous‐Flow Reactor**

Ioannou,

Capaldo,

Sanramat

et al. 2023

Angew Chem Int Ed

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Electrophotocatalytic transformations are garnering attention in organic synthesis, particularly for accessing reactive intermediates under mild conditions. Moving these methodologies to continuous‐flow systems, or flow ElectroPhotoCatalysis (f‐EPC), showcases potential for scalable processes due to enhanced irradiation, increased electrode surface, and improved mixing of the reaction mixture. Traditional methods sequentially link photochemical and electrochemical reactions, using flow reactors connected in series, yet struggle to accommodate reactive transient species. In this study, we introduce a new flow reactor concept for electrophotocatalysis (EPC) that simultaneously utilizes photons and electrons. The reactor is designed with a transparent electrode and employs cost‐effective materials. We used this technology to develop an efficient process for electrophotocatalytic heteroarylation of C(sp3)–H bonds. Importantly, the same setup can also facilitate purely electrochemical and photochemical transformations. This reactor represents a significant advancement in electrophotocatalysis, providing a framework for its application in flow for complex synthetic transformations.

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“…27 Photochemical reactions can also be used for the protection of alcohols, where they are transformed into acetals. 28 Furthermore, quinolines 29,30 or biphenyl chromophores 31 were developed and their applicability to decage carboxylic acid under two photon excitations has been demonstrated. Moreover, some elegant examples of photocages base their molecular design on indenes 32 and the antiaromatic character of 6π systems in the excited states.…”

Section: Introductionmentioning

confidence: 99%

“…The decaging of alcohols was also reported by the use of 2,5-dimethylphenacyl photocages . Photochemical reactions can also be used for the protection of alcohols, where they are transformed into acetals . Furthermore, quinolines , or biphenyl chromophores were developed and their applicability to decage carboxylic acid under two photon excitations has been demonstrated.…”

Section: Introductionmentioning

confidence: 99%

3-Substituted 2-Aminonaphthalene Photocages for Carboxylic Acids and Alcohols; Decaging Mechanism and Potential Applications in Synthesis

Lovrinčević,

Guo,

Vuk

et al. 2023

J. Org. Chem.

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3-Hydroxymethyl-2-aminonaphthalene photocage (photoremovable protecting group) 2 was synthesized and transformed to different ethers and esters to investigate the applicability to decage alcohols and carboxylic acids, respectively. The photoelimination of carboxylic acids takes place relatively efficiently (Φ R = 0.11) upon excitation with near-visible light, contrary to the elimination of alcohols. The scope of the decaging of both alcohols and esters was demonstrated on several examples, including aliphatic and aromatic substrates, carbohydrates, and nonsteroidal anti-inflammatory drugs. The photophysical properties of the photocage and its models, methyl ether 4a and acetyl ester 5a, were investigated. The fluorescence quantum yields (Φ f = 0.40− 0.002) were found to be reversely proportional to the efficiency of elimination of OH, alcohols, or carboxylic acids. The decaging photochemical reaction mechanism was investigated experimentally by transient absorption techniques with time scales from femtoseconds to seconds and computationally on the TD-DFT level of theory. The photoelimination of carboxylates takes place directly in the singlet excited state by a homolytic cleavage producing a radical pair within 1 ns. The subsequent electron transfer gives rise to aminonaphthalene carbocation and the carboxylate. A wide scope of substrates that can be decaged relatively efficiently with near-visible light and the chromo-orthogonal compatibility of aminonaphthalene and aniline derivatives render these photocages potentially applicable in organic synthesis or biology.

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Photochemical C–H acetalization of O-heterocycles utilizing phenylglyoxylic acid as the photoinitiator

Cited by 10 publications

References 51 publications

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

Accelerated Electrophotocatalytic C(sp³)−H Heteroarylation Enabled by an Efficient Continuous‐Flow Reactor**

3-Substituted 2-Aminonaphthalene Photocages for Carboxylic Acids and Alcohols; Decaging Mechanism and Potential Applications in Synthesis

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Photochemical C–H acetalization of O-heterocycles utilizing phenylglyoxylic acid as the photoinitiator

Cited by 10 publications

References 51 publications

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

Accelerated Electrophotocatalytic C(sp3)−H Heteroarylation Enabled by an Efficient Continuous‐Flow Reactor**

3-Substituted 2-Aminonaphthalene Photocages for Carboxylic Acids and Alcohols; Decaging Mechanism and Potential Applications in Synthesis

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Product

Resources

About

Accelerated Electrophotocatalytic C(sp³)−H Heteroarylation Enabled by an Efficient Continuous‐Flow Reactor**