4.6- Dinitrobenzofuroxan substitution with

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... 

It should also be mentioned that NO2 is the electron-attracting substituent which is most commonly used to stabilize Meisenheimer-type complexes. See, for example, recent studies of the reaction of 1,3,5-trinitrobenzene and phenoxide ions215, and the reactions of 4,6-dinitrobenzofuroxan with 5-substituted indoles216. See also the appropriate chapter in each year of the Series Organic Reaction Mechanisms1 1. 

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. 

Picryl chloride (87) reacts with hydroxylamine hydrochloride to yield 2,4,6-trinitroaniline (53) (picramide) and not the expected At-hydroxy-2,4,6-trinitroaniline. In contrast, the same reaction in the presence of sodium ethoxide is reported to yield 4,6-dinitrobenzofuroxan (94) via substitution of the halogen by hydroxylamine, followed by an internal redox reaction between the hydroxyamino group and one of the adjacent o-nitro groups. ... 

There have been several studies utilizing the ability of 4,6-dinitrobenzofuroxan (DNBF) to act as a super-electrophile. It has been shown that the initial product of its reaction with phenoxide ions is the O-bonded adduct (29), although this rearranges to give die C-bonded adduct.117 The reaction of DNBF with ethyl vinyl ether yields a dihydrooxazine A -oxidc cycloadduct as a mixture of two diastereoisomers, and in the presence of excess ether a di-adduct (30) is formed.118 Rate constants have been reported for the reaction of DNBF with 3-methoxythiophene in DMSO-water mixtures. The reaction results in a er-adduct which is the product of Se-At substitution in the thiophene, and the results were used to probe the carbon basicity of the thiophene derivative.119... 

The reaction of 7-chloro-4,6-dinitrobenzofurazan with 2-(4,-bromophenyl)indolizine has been shown to result in carbon-carbon bond formation by substitution of the 7-chloro substituent.58 However, in the reaction of 7-chloro-4,6-dinitrobenzofuroxan the initial substitution is followed by intramolecular oxygen transfer from the N-oxide function and by rearrangement to give the zwitterionic spiro-adduct (15). An... 

Studies of the reactivity of 4,6-dinitrobenzofuroxan with substituted indoles have been mentioned above.49... 

A DFT study of the molecular orbitals of pyridine and a number of heteroaromatics unreactive to electrophilic substitution shows that the HOMOs of these compounds are not r-orbitals and so their low reactivity can be explained by assuming frontier orbital control of their substitution reactions.1 Consistent with this rationalization is the fact that in the case of pyridine-A-oxide and a number of other reactive substrates the HOMOs are n-orbitals. 4,6-Dinitrobenzofuroxan (1) is a superelectrophile and reacts with some supernucleophilic l,3,5-tris(A,A-dialkylamino)benzenes to form the first observed Meisenheimer-Wheland zwitterionic complexes [e.g. (2)].2... 

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. 

The SNAr reactions of heteroarenes can be realized in a similar manner, as in the series of arenes [71, 82]. These nucleophilic reactions are analogous to electrochemical Sn transformations of arenes [22, 24, 25]. Terrier and co-workers considered an opportunity for electrochemical methoxylation of 4,6-dinitrobenzofuroxan by action of the methoxide ion via the SnAt mechanism [21]. The intermediate o -complex formed was oxidized successfully into the corresponding substitution product. Analogously, the formation of heteroaromatic amines has been suggested to occur via intermediacy of the corresponding amino adducts, as exemplified by the oxidation of the o -complex derived fi om the reaction of pyrimidine with NH2 (Scheme 26) [3, 102-104]. 

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. 

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