Transition Metal‐Mediated Direct CH Arylation of Heteroarenes Involving Aryl Radicals

Abstract

This review gives an overview of the generation of aryl radicals, mediated by transition metals, and their use for the C À H arylation of heteroarenes. The different sources of aromatic derivatives able to generate aryl radicals via a metal-assisted reduction or oxidation are discussed, with a critical view of the developed systems. The radical arylations of nitrogen-, oxygen-or sulfur-containing heterocycles are then described and mechanistic considerations are discussed as well.

Retraction of “Ascorbic Acid-Promoted C–H Arylation of Heterocyclic N-Oxides through in Situ Diazotisation of Anilines: A Green and Selective Coupling Process”

“…Whilst not exhaustive, this initial series of heterocyclic N-oxides suggested this transformation should have significantly broader scope than the single example reported by Carrillo et al 34 and provided a number of interesting trends that warranted further investigation. These promising preliminary results encouraged us to screen different organic solvents in order to evaluate the impact of the reaction medium on the yield 11). Amongst all the solvents screened, acetonitrile gave the product in 60% isolated yield and was therefore found to be optimal for this metal free arylation reaction ( to find the multidimensional direction in the solvent descriptors space that explains the maximum variance in the yield (Figure 2a).…”

“…10 A potentially more sustainable approach is the direct arylation of aromatic rings employing an aryl radical species generated in-situ. 11,12 Aryl radical species 1 can be obtained from the corresponding arylboronic acids 2, [13][14][15][16] arylhalides 3, 17 aryldiazonium salts 4 [18][19][20][21] and diaryliodonium salts 5 [22][23][24] (Figure 1). Addition of the aryl radical to a second aryl species followed by oxidation / rearomatisation then Figure 1.…”

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

“…Synthetic methods for the construction of aryl–aryl bonds are mainly based on transition‐metal catalysis, including Suzuki, Stille, and Ullmann couplings, and biaryls may as well be obtained through C−H activation reactions, oxidative coupling reactions, and reactions via arynes . 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 .…”

UiO‐66 microcrystals catalyzed direct arylation of enol acetates and heteroarenes with aryl diazonium salts in water

“…[1,2] As an ideal generator of aryl radicals, aryl diazonium salts have attracted more and more attention in cross coupling, C-H-arylation and annulation reactions. [2][3][4][5][6][7] Particularly, direct arylation of enol acetates and heteroarenes with aryl diazonium salts is of significant importance since the arylated products are ubiquitous with diverse applications. [8] However, the reported procedures usually suffered from the drawbacks of homogeneous transition metal catalysts such as CuCl in Meerwein arylation, unfriendly solvents and unsatisfactory yields.…”