4.6- Dinitrobenzofuroxan anilines

Nucleophilic displacement of a nitro group by aniline in 5,6-dinitrobenzofuroxan has been reported. Rearrangements of 4-nitro-benzofuroxans are discussed in Section VIII. 

Several examples of nucleophilic displacement of nitro-activated leaving groups have been recorded. 5,6-Dinitrobenzofuroxan with aniline and p-bromoandine gives the corresponding substitution product (50). Azide ion displaces chloride from both 5-chloro-4-nitro- and 4-chloro-7-nitrobenzofuroxan (51 and 52) the product from the former loses nitrogen spontaneously to give furoxanobenzo-furoxan (benzobisfuroxan, 17), which is also formed, although in poor... 

The photometric determination of mixtures of aniline, p-nitroaniline and o-nitroaniline was described. Distribution coefficients and separation efficiency of these compounds by LLE in various solvents were compared517. Substituted nitroanilines such as 2-chloro-4-nitroaniline and 2,4-dinitroaniline are intermediates in the manufacture of the dye D C Red No. 36 and were identified as impurities by RP-LC518. A spectrophotometric method was developed for the determination of aniline and m-nitroaniline in a mixture of aniline and nitroaniline isomers by derivatization with 5,7-dichloro-4,6-dinitrobenzofuroxan (244). The relative error of the determination is <5%519. See also Section IV.D.3.b for similar derivatives. 

Aminothiazole and its 4-methyl derivative react with the superelectrophilic 4,6-dinitrobenzofuroxan at C(5) to form, for example, (1) in spite of them exhibiting higher nitrogen basicity than aniline.7 In the case of 4,5-dimethyl-2-aminothiazole, however, attack did occur at nitrogen. 

S Ar reactions have been studied mostly with dinitro and trinitro activated benzenes. Recently, the aniline reactions with the highly activated super-electrophile, 4,6-dinitrobenzofuroxan (DNBF), have attracted considerable attention due to its ambident reactivity114. In acidic solvent, where aniline is almost completely protonated, the reaction by nitrogen attack is inhibited. However, a carbon-carbon bonded adduct is slowly formed by reaction at the 4-position of the aniline. Kinetic studies in H2O-DMSO have shown that this adduct formation involves two steps a carbon-carbon bond formation ( a), followed by elimination of a proton, Kiep (vide infra). The reactions of anilines with DNBF in DMSO have shown that the N-bonded adduct (a-N) is kinetically preferred, but the C-bonded adduct (a-C), formed in equilibrium with its deprotonated form, is the thermodynamically favored product (Scheme 14). 

This study reports on the reactions of ambident nucleophiles with electron-deficient nitroaromatic and heteroaromatic substrates anionic complex formation or nucleophilic substitution result. Ambident behavior is observed in the case of phenoxide ion (O versus C attack) and aniline (N versus C attack). O or N attack is generally kinetically preferred, but C attack gives rise to stable thermodynamic control. Normal electrophiles such as 1,3,5-trinitrobenzene or picryl chloride are contrasted with superelectrophiles such as 4,6-dinitrobenzofuroxan or 4,6-dinitro-2-(2,4,6-trinitrophenyl)benzotriazole 1-oxide (PiDNBT), which give rise to exceptionally stable a complexes. Further interesting information was derived from the presence in PiDNBT of two electrophilic centers (C-7 and C-l ) susceptible to attack by the ambident nucleophilic reagent. The superelectrophiles are found to exhibit lesser selectivity toward different nucleophilic centers of ambident nucleophiles compared with normal electrophiles. 

There is continued interest in the super-electrophile4,6-dinitrobenzofuroxan (DNBF). Reaction in DMSO with aniline, which may show ambident nucleophilic character, initially yields the nitrogen-bound adduct (18) and then, more slowly, the carbon-bound adduct (19) in which the DNBF has effected electrophiUc substitution of hydrogen. 

An ab initio smdy suggests that the formation of a Diels-Alder adduct [i.e. (23)] from reaction between 1-methylpyrrole and dimethyl acetylenedicarboxylate is favoured over the formation of a possible Michael-type addition product (24). Both pathways involve an initial electrophilic substitution at the 2-position of the pyrrole to form a zwitterionic intermediate. A review, in Chinese, concerns a number of electrophilic substitutions of pyridine. A kinetic study has been made of the reaction between 4,6-dinitrobenzofuroxan (25) and various anilines in acidic H2O-DMSO... 

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