“Transition-Metal-Free” Synthesis of Carbazoles by Photostimulated Reactions of 2′-Halo[1,1′-biphenyl]-2-amines

Abstract

An efficient and simple protocol for the preparation of a series of 9H-carbazoles by photostimulated SRN1 substitution reactions is presented. Substituted 9H-carbazoles were synthesized in low to excellent yields (up to 96%) through an intramolecular C–N bond formation of 2′-halo[1,1′-biphenyl]-2-amines by the photoinitiated SRN1 mechanism under mild and “transition-metal-free” conditions. The biphenylamines used as substrates were obtained with isolated yields ranging from 21% to 84% by two approaches: (A) the cross-coupling Suzuki–Miyaura reaction and (B) the radical arylation of anilines. Some key aspects of the proposed mechanism were evaluated at the B3LYP/6-311+G* level.

Nano-cuprous oxide catalyzed one-pot synthesis of a carbazole-based STAT3 inhibitor: a facile approach via intramolecular C–N bond formation reactions

“…The complex A further reacts with base to form Cu-N bond to form complex B. Reductive elimination step regenerates the copper catalyst and formation of the desired product C. Our findings suggested that secondary amines were more liable for cyclisation compare to primary amines 25,44 wherein poor ring formation was observed in the reaction carried out without using benzylbromide (2a) (Scheme 2), which apparently support N-benzylation occurs before the coordination of the copper complex with amine nitrogen.…”

Transition‐Metal‐Free Synthesis of Acridones via Base‐Mediated Intramolecular Oxidative C−H Amination

“…[9] Lei described an approach to acridones through palladium/copper co-catalyzed oxidative carbonylation of diphenylamines. [11] However, the halo substitued substrates were necessary for the reaction. In 2015, Barolo successfully developed a photo-initiated S RN 1 protocol for the synthesis of substituted 9H-carbazoles using 2'-halo[1,1'-biphenyl]-2-amines under mild and transition-metal-free conditions.…”

“…Other solvents, such as dioxane, ClCH 2 CH 2 Cl, CH 3 CN, THF, dimethoxyethane, and glycol were unsuccessful in this reaction with no desired product obtained (see Table S1, entries [9][10][11][12][13][14]. N,Ndimethylacetamide (DMA), N,N-dimethylformamide (DMF), and toluene were applicable.…”

Transition‐Metal‐Free Synthesis of Carbazoles and Indoles by an SNAr‐Based “Aromatic Metamorphosis” of Thiaarenes

“…Liu and Knochel disclosed that halogen-magnesium exchange of 2-iodo-2'-triazenobiaryls resulted in formation of carbazoles. [10] Kürti and co-workers disclosed facile reductive cyclization of 2-nitrobiaryls by means of PhMgBr. [7] Studer and coworkers invented an interesting approach, that is,reactions of arynes with nitrosoarenes, [8] but the yields were moderate and the regioselectivity was not as well controlled as is typically observed in aryne chemistry.T okuyama and co-workers developed ab ase-mediated cyclization of 2-amino-2'-bromobiphenyls via arynes.…”

“…[6] Theg roups of Chang and Antonchick reported intramolecular oxidative C À Ha mination of amino-biaryls with hypervalent iodine reagents. [10] Kürti and co-workers disclosed facile reductive cyclization of 2-nitrobiaryls by means of PhMgBr. [9] From similar precursors,photoinduced cyclization occurs by ar adical process to yield carbazoles.…”