Visible-Light Photocatalytic Reduction of Aryl Halides as a Source of Aryl Radicals

Abstract

Aryl- and heteroaryl units are present in a wide variety of natural products, pharmaceuticals, and functional materials. The method for reduction of aryl halides with ubiquitous distribution is highly sought after for late-stage construction of various aromatic compounds. The visible-light-driven reduction of aryl halides to aryl radicals by electron transfer provides an efficient, simple, and environmentally friendly method for the construction of aromatic compounds. This review summarizes the recent progress in the generation of aryl radicals by visible-light-driven reduction of aryl halides with metal complexes, organic compounds, semiconductors as catalysts, and alkali-assisted reaction system. The ability and mechanism of reduction of aromatic halides in various visible light induced systems are summarized, intending to illustrate a comprehensive introduction of this research topic to the readers.

Recyclable Mesoporous Graphitic Carbon Nitride Catalysts for the Sustainable Photoredox Catalyzed Synthesis of Carbonyl Compounds

“…Surprisingly, even 4-iodoethylbenzene was oxidized to give 4-iodoacetophenone in 73% yield, whereas typically, under photochemical conditions, iodobenzenes are not tolerated and often result in deiodinated products. 58 It is worth mentioning that not only electron-rich but also electrondeficient and heterocyclic substrates are suitable for this transformation (54, 58−60). The late-stage modification of C−H bonds in ethylbenzene is an atom-economical strategy.…”

“… , Alkyl arenes, both acyclic and cyclic, were selectively oxidized to yield the desired products in up to 93% yield (Figure ). Surprisingly, even 4-iodoethylbenzene was oxidized to give 4-iodoacetophenone in 73% yield, whereas typically, under photochemical conditions, iodobenzenes are not tolerated and often result in deiodinated products . It is worth mentioning that not only electron-rich but also electron-deficient and heterocyclic substrates are suitable for this transformation ( 54 , 58 – 60 ).…”

Radical Substitution of Polyfluoroarenes and Heteroarenes Promoted by Photoredox Activation of Organozinc Iodides

“…The most common pathway is based on the generation of aryl radicals via reduction of the substrate followed by coupling with nucleophiles or π-systems [9,10] (Scheme 1A, top path). This works well with diazonium ions, [11][12][13] and other electron deficient aryl halides, [14][15][16][17] including perfluorinated aromatics. [18][19][20] For electron rich aromatic substrates, the reaction may start from oxidation with subsequent nucleophilic addition (middle path).…”

Photocatalyst‐ and Transition‐Metal‐Free Light‐Induced Formation of Carbon‐Chalcogen Bonds

“…This excited state transferred energy to triplet oxygen 3 O 2 , producing the more active excited-state singlet oxygen 1 Utilizing aryl halides (Cl, Br and I) as an aryl radical source under photocatalytic conditions for diverse CÀ C and C-heteroatom bond formations were extensively explored in organic synthesis. [28] In this context, Wu and co-workers showcased the synthesis of alcohols and phenols 2 b from organic halides 2 a under photocatalyst-free conditions, with O 2 acting as the oxygen source (Scheme 2). [29] After an extensive screening of solvents, additives, and amines, the authors determined the optimal reaction conditions.…”