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4.6- Dinitrobenzofuroxan nucleophiles

Nitration of benzofuroxans (Section VII, A) and decomposition of polynitrophenyl azides, provide generally satisfactory routes to nitrobenzofuroxans. The nitro groups render the ring susceptible to nucleophilic attack (see Section VII,B). 4,6-Dinitrobenzofuroxan, 5,6-dinitrobenzofuroxan, and nitrobenzodifuroxan (34) act as acceptors in change-transfer complex formation with aromatic hydrocarbons. Nitrobenzofuroxans have not been reduced to the... [Pg.19]

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. [Pg.19]

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... [Pg.25]

Nucleophilic reactions take place in the homocyclic ring, SwAr or AEc when it is activated by electron-withdrawing substituents. It has been described that halides can be displaced by a great number of nucleophiles via a normal and cine substitution [54,55]. Nitro containing Bfx has represented a class of neutral lO-TT-electron-defident system which exhibit an extremely high electrophilic character in many covalent nucleophihc addition and substitution processes. 4,6-Dinitrobenzofuroxan and others 4-nitro-6-substitutedbenzofuroxans (Scheme 2) have been defined as superelectrophiles and used as convenient probes to assess to the C-basicity of... [Pg.273]

The very strong tendency of 4,6-dinitrobenzofuroxan (160) to react with nucleophiles has long been known. As early as 1899 Drost found that 160 reacts reversibly with aqueous alkalies to yield explosive salts.197... [Pg.425]

Dinitrobenzofuroxan (160) is such a powerfully activated substrate toward nucleophiles that it can react with unionized water in the appropriate pH range. A complete quantitative investigation of the reactions occuring in aqueous solution was carried out by Terrier et al.221,222 through the changes in absorbance at 465 nm between pH 1 and 13. The measurements of the reaction rates required the use of the stopped-flow technique. [Pg.430]

For the most reactive compounds in the series, i.e., 4,6-dinitro-benzofurazans and 4,6-dinitrobenzofuroxans, not only water222 but also methanol220 is found to be an effective neutral nucleophile in the appropriate pH range. The thermodynamic and kinetic analysis for the reactions in methanol similar to that described above for the reactions in water has been applied to the formation of 172 from 4,6-dinitro-7-methoxybenzofurazan (195) in the pH range from 2.2 to 14. The formation of 172 has been followed spectrophotometrically and found to be complete in methanol. The reaction scheme is as follows... [Pg.434]

Dinitrobenzofuroxan (DNBF) is known as a superelectrophile due to its high reactivity both as an electrophile and in its pericyclic addition reactions. NMR studies show that reaction with 2-aminothiazole and its 4-methyl derivative yield anionic carbon-bonded adducts such as (11) by reaction at the 5-position, whereas the 4,5-dimethyl derivative reacts via the exocyclic amino group. Kinetic studies of the first two compounds, both in acetonitrile and in 70 30 (v/v) water-DMSO, have been used to assess their carbon nucleophilicities and place them on the Mayr nucleophilicity scale.55 In a related study, the nucleophilic reactivity, in acetonitrile, of a series of indoles with both DNBF and with benzhydryl cations have been compared and used to determine nucleophilicity parameters for the indoles.56... [Pg.183]

There is evidence for formation of a zwitterionic Meisenheimer-Wheland complex between superelectrophilic and supernucleophilic reagents. Thus, NMR spectra in CD2CI2 show the formation of (12) from 4,6-dinitrobenzofuroxan and l,3,5-lris(/V,/V-dialkylamino)benzenes. At temperatures above — 30 °C the spectra show the presence of a dynamic process interconverting the three equivalent ring positions of the nucleophile.51... [Pg.161]

Potentiometric measurements indicate that in water-DMSO the 3-aminothiophenes 197 undergo protonation exclusively at the nitrogen with dilute acid. But on treatment with the superelectrophile 4,6-dinitrobenzofuroxan (DNBF) they react as carbon nucleophiles giving rise directly to the corresponding C-adducts. The 3-aminothio-phenes are thus shown to possess strong enaminic character <1998CJC937>. [Pg.808]

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. [Pg.361]

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]. [Pg.270]

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. [Pg.289]

The high electrophilicities of 4,6-dinitrobenzofuroxan (DNBF) and 4,6-dinitrotetrazo-lopyridine place them in the superelectrophile category. Their reactions in acetonitrile with 2,4-dipyrrolidin-l-yl-l,3-thiazole, a strong nucleophile, allow the isolation of zwitterionic Meisenheimer-Wheland complexes, which are stable enough for X-ray... [Pg.217]


See other pages where 4.6- Dinitrobenzofuroxan nucleophiles is mentioned: [Pg.284]    [Pg.293]    [Pg.251]    [Pg.425]    [Pg.427]    [Pg.560]    [Pg.691]    [Pg.113]    [Pg.568]    [Pg.577]    [Pg.26]    [Pg.578]    [Pg.142]    [Pg.158]   
See also in sourсe #XX -- [ Pg.97 , Pg.253 ]




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4.6- Dinitrobenzofuroxan reactions with nucleophiles

Dinitrobenzofuroxan

Dinitrobenzofuroxane

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