Copper-catalyzed free-radical C–H arylation of pyrroles

Abstract

A room temperature copper-catalyzed radical arylation of pyrroles with anilines, through in situ generated aryl diazonium salts, has been developed under neutral conditions. Experimental and theoretical studies explain the crucial role of CaCO3 and the high regioselectivity observed.

Graphite-supported ultra-small copper nanoparticles – Preparation, characterization and catalysis applications

“…This copper-catalyzed reaction was recently optimized in our laboratory using copper(II) acetate as a homogeneous catalyst and acetone/water as solvent system. [66] We were pleased to find that the use of Cu Furthermore, the catalytic performances of 5% Cu NPs/Gr catalyst were investigated for the Huisgen 1,3-dipolar cycloaddition of organic azides with alkynes, [67,68] independently discovered by Medal and Sharpless. [69,70] This reaction is a leading transformation in the arsenal of synthetic chemists that found numerous applications in chemical-biology [71] and material chemistry.…”

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

“…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.…”

“…[25][26][27] Although conceptually simple, a major limitation of this transformation arises when the aryl radical is reacted with complex aromatics, leading to chaotic additions and mixtures of regioisomeric products. 28 For example, whereas unsubstituted heterocyclic substrates such as furan, thiophene and pyrrole exclusively led to the 2-arylated product, 18,20,22,23 reactions with pyridine provided a mixture of regioisomers, albeit in reasonable yields. Along with problems arising due to the high reactivity of the aryl radical intermediates, an additional challenge is the handling of the potentially unstable aryl diazonium precursors.…”

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

“…[60] When we started our studies, the metal-catalyzed arylation of pyrroles with diazonium salts was unknown since their high nucleophilicity strongly favoured the addition over the diazonium function, leading to the corresponding azo compound. This unwanted process was even reinforced in the acidic conditions required for the Meerwein arylation (pH < 3).…”