Nucleophilic aromatic substitution diphenylamines

The reactions between 2,4-dinitrohalogenobenzenes and X-substituted anilines in benzene produce the usual diphenylamines 109 by nucleophilic aromatic substitution reaction 28. The inspection of reaction mixtures by UV/VIS spectroscopy at zero reaction... 

Most syntheses of naturally occurring phenazines, though, are based on a two-step elaboration of the central heterocycle of the phenazine [78]. The first key step involves the generation of orf/zo-monosubstituted 88 or orf/zo, ortho -disubstituted diphenylamines 89-91 via nucleophilic aromatic substitution. Ring formation is then achieved by means of reductive or oxidative cyclization, for which a number of efficient methods are available. The main flaw of this approach is the synthesis of the substituted diphenylamines via nucleophilic aromatic substitution, as this reaction often can only be performed under strongly basic reaction conditions and at high temperatures. In addition, the diphenylamines required may only be achieved with certain substitution patterns with high yields. 

Nucleophilic displacements on unsubstituted aromatics usually do not occur since H is not a good leaving group. However, an example of nucleophilic aromatic substitution of hydrogen (NASH) has been reported on reacting aniline and azobenzene in the presence of base under aerobic conditions to generate 4-(phenylazo)diphenylamine, 9 (equation 13)115. 

Although diselenonium-, ditelluronium- and mixed sulfonium-selenonium dications can exhibit either oxidative or electrophilic properties in reactions with nucleophiles, substitution at the onium chalcogen atom is more typical.96 Owing to the increased stability of heavier dichalcogenium-dications, they react only with highly activated substrates such as aniline and tV,A-dimethylaniline, while no reaction is observed with phenol and diphenylamine.113 Reactions of ditelluronium dications with activated aromatics are also not known (Scheme 44).114... 

The major pathways for the anodic oxidation of diarylamines are N,N- or aryl,aryl-coupling, A,aryl-coupling, and nucleophilic substitution in the aromatic ring. Which pathway actually will be followed depends on the reaction conditions and the substitution pattern of the substrate. With regard to the latter, one has to distinguish between p-unsubstituted, p-mono- and / -disubstituted diphenylamines. 

There has been a major review of substitution by the radical-chain 5rn1 mechanism. It has been shown that reaction by the SrnI pathway of the enolate anions of 2- and 3-acetyl-l-methylpyrrole may yield a-substituted acetylpyrroles. The dichotomy of reactions of halonitrobenzenes with nucleophiles has been nicely summarized major pathways include reduction via radical pathways and. SnAt substitution of halogen. EPR spectroscopy has been used to detect radical species produced in the reactions of some aromatic nitro compounds with nucleophiles however, whether these species are on the substitution pathway is questionable. The reaction of some 4-substimted N,N-dimethylanilines with secondary anilines occurs on activation by thallium triacetate to yield diphenylamine derivatives radical cation intermediates are proposed. ... 

---