Mild, visible light-mediated decarboxylation of aryl carboxylic acids to access aryl radicals

Candish, Lisa; Freitag, Matthias; Gensch, Tobias; Glorius, Frank

doi:10.1039/c6sc05533h

Cited by 154 publications

(100 citation statements)

References 57 publications

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“…Radical‐based transformations, which are a further alternative for biaryl synthesis, have recently received attention through new developments in the field of catalysis, particularly photocatalysis . Such photocatalyzed reactions can be conducted with a number of aryl radical precursors including diazonium and iodonium salts, diazoanhydrides, carboxylic acids, azo sulfones, and iodo‐, bromo‐, and chloroarenes . Typically employed photocatalysts are complexes of ruthenium or iridium, eosin Y, titanium dioxide,, or strong electron donors, and double excitation of perylene bisimide recently allowed the conversion of aryl chlorides …”

Section: Methodsmentioning

confidence: 99%

Visible‐Light‐Induced, Catalyst‐Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

Fürst

Gans

Bock

et al. 2017

Chemistry A European J

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In the absence of a photocatalyst and other additives, the radical arylation of diverse arenes and heteroarenes has been achieved with aryldiazonium salts under visible-light irradiation from a blue light-emitting diode (LED). Although the course of some reactions can be rationalized by the formation of strongly light-absorbing charge-transfer (CT) complexes between the diazonium ion and the aromatic substrate, several further examples indicated that the simple presence of an aromatic substrate, showing only weak interactions to the diazonium ion, is fully sufficient to enable product formation.

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Section: Methodsmentioning

confidence: 99%

Visible‐Light‐Induced, Catalyst‐Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

Fürst

Gans

Bock

et al. 2017

Chemistry A European J

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“…[4] In combination with av isible-light photoredox catalysis, structurallyd istinct HATcatalysts, such as thiols, [5] thiophosphoric acids and imides, [6] quinuclidines, [7] sulfonamides, [8] chloride [9] and bromide [10] ions, aryl carboxylates, [11] and N-hydroxy compounds [12] wered eveloped. The currently-available HAT catalysts have limitations,s uch as:1)limited scope of cleavable CÀHb onds; [13] 2) catalystd ecomposition due to the inherent nucleophilicity [14] and/or reactivity with carbon-carbonm ultiple bonds; [15] and 3) insufficient stability, [16] thus leaving room for improvement. HATcatalysts that can cleave C(sp 3 )ÀHb onds with ar elatively high bond-dissociation energy (BDE:9 5-105 kcal mol À1 )a nd high catalyst turnover are in high demand.…”

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confidence: 99%

C(sp³)−H Cyanation Promoted by Visible‐Light Photoredox/Phosphate Hybrid Catalysis

Wakaki

Sakai

Enomoto

et al. 2018

Chemistry A European J

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Inspired by the reaction mechanism of photo-induced DNA cleavage in nature, a C(sp )-H cyanation reaction promoted by visible-light photoredox/phosphate hybrid catalysis was developed. Phosphate radicals, generated by one-electron photooxidation of phosphate salt, functioned as a hydrogen-atom-transfer catalyst to produce nucleophilic carbon radicals from C(sp )-H bonds with a high bond-dissociation energy. The resulting carbon radicals were trapped by a cyano radical source (TsCN) to produce the C-H cyanation products. Due to the high functional-group tolerance and versatility of the cyano group, the reaction will be useful for realizing streamlined building block syntheses and late-stage functionalization of drug-like molecules.

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“…Visible-light photoredox catalysis is emerging as apowerful tool in organic synthesis and involves the generation of radical intermediates. [8] Thus,t he proposed aryl migration would occur by the initial generation of an aryl carboxylic radical intermediate A by visible-light redox catalysis with ac atalytic base, [9] followed by formation of the cyclic intermediate B to afford the final product 2a (Scheme 2). [3] Theformation of the more stable ester C À Obond should be the driving force of this aryl migration, as the CÀOb ond energies of an aryl ether and an ester are about 78.8 and 87-93 kcal mol À1 ,respectively.…”

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confidence: 99%

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

Wang

Cao

2017

Angewandte Chemie

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We have developed ahighly efficient aryl migration from an aryl ether to ac arboxylic acid group through retro-Smiles rearrangement by visible-light photoredoxc atalysis at ambient temperature.T ransition metals and as toichiometric oxidant and base are avoided in the transformation. Inspired by the high efficiency of this transformation and the fundamental importance of C À Ob ond cleavage,w ed eveloped anovel approachtothe C À Ocleavage of abiaryl ether to form two phenolic compounds,a sd emonstrated by ao ne-pot, twostep gram-scale reaction under mild conditions.T he aryl migration exhibits broad scope and can be applied to the synthesis of pharmaceutical compounds,s uch as guacetisal. Primary mechanistic studies indicate that the catalytic cycle occurs by ar eductive quenchingpathway.Various aryl-migration reactions have been developed and display broad application. [1] Notably,a ryl migration from an aryl ether to form an ester is rare.In1955, this migration was first observed upon the thermal decomposition of 2-phenoxybenzoyl peroxide in 25 %y ield by DeTar and Hlynsky. [2] Recently,t he migration was promoted by silver catalysis at 130 8 8CbyHossian and Jana, who used acarboxylic acid as the starting material. [3] However,t he stoichiometric strong oxidant K 2 S 2 O 8 and ab ase were required. Furthermore,t he transformation only resulted in up to 64 %y ield. No clear electronic effects on this aryl migration were observed. Thus, the transformation was identified as aSmiles rearrangement. Herein, we demonstrate ahighly efficient aryl migration from an aryl ether to form the ester of acarboxylic acid by visiblelight photoredox catalysis at ambient temperature without an oxidant [Scheme 1, Eq. (1)].O nly 1mol %o faphotosensitizer (PDI or Acr + -Mes ClO 4 À )a nd 10 mol %o fabase (K 2 HPO 4 )w ere required. Notably,e lectron-donating groups on the migrating aryl ring generally induced higher yields in this transformation, which differs from the typical Smiles rearrangement [4] and can be understood as ar etro-Smiles rearrangement. [4a,5] As this developed aryl migration is the retro-reaction of the reported Smiles rearrangement involving aryl migration from an ester to form an aryl ether. [6] And the Smiles rearrangement always requires ah eteroatom as the nucleophilic component and an electrophilic arene activated by strong electron-withdrawing groups,acarbonbased nucleophile,orfree-radical attack on the ipso-position of sulfonates or sulfonamides. [4] By taking advantage of visible-light photoredox catalysis,transition metals and astoichiometric amount of an oxidant and abase are avoided, thus leading to an environmentally benign and highly atom economical transformation. Moreover,i nspired by the high efficiency of this aryl migration and the fundamental importance of CÀOb ond cleavage, [4i, 7] we demonstrate an ovel approach to CÀOb ond cleavage in biaryl ethers to give two phenolic compounds in ao ne-pot, two-step reaction under mild conditions as as ubsequent transformation [Scheme 1, Eq. (2)].Visible...

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Mild, visible light-mediated decarboxylation of aryl carboxylic acids to access aryl radicals

Abstract: Herein we present the first example of aryl radical formation via the visible light-mediated decarboxylation of aryl carboxylic acids using photoredox catalysis.

Cited by 154 publications

References 57 publications

Visible‐Light‐Induced, Catalyst‐Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

Visible‐Light‐Induced, Catalyst‐Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

C(sp³)−H Cyanation Promoted by Visible‐Light Photoredox/Phosphate Hybrid Catalysis

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

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Mild, visible light-mediated decarboxylation of aryl carboxylic acids to access aryl radicals

Abstract: Herein we present the first example of aryl radical formation via the visible light-mediated decarboxylation of aryl carboxylic acids using photoredox catalysis.

Cited by 154 publications

References 57 publications

Visible‐Light‐Induced, Catalyst‐Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

Visible‐Light‐Induced, Catalyst‐Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

C(sp3)−H Cyanation Promoted by Visible‐Light Photoredox/Phosphate Hybrid Catalysis

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

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C(sp³)−H Cyanation Promoted by Visible‐Light Photoredox/Phosphate Hybrid Catalysis