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4.6- Dinitrobenzofuroxan reactions, with

Spectroscopic and kinetic investigations of the reactions between 4,6-dinitrobenzofuroxan, 4-nitrobenzofuroxan, and tertiary and secondary amines (i.e., l,4-diazabicyclo[2.2.2]octane, quinuclidine, l,8-diazabicyclo[5.4.0]undec-7-ene, and piperidine) indicate the formation of zwitterionic or anionic complexes (Equation 2). The equilibrium between zwitterionic and anionic complexes is discussed (for reaction with piperidine) on the basis of H NMR spectral data, which indicate the presence of anionic complexes arising from the zwitterionic complex by a fast proton departure. The stability and the rate of formation of title complexes are discussed and compared to similar reactions of 1,3,5-trinitrobenzene <2001J(P2)1408>. [Pg.321]

Some interesting reactions of the super-electrophile 4,6-dinitrobenzofuroxan (151) with aryloxide ions have been reported 130 (151) with phenoxide ion gives the O-bonded ff-adduct (152) which has been fully characterized for the first time. On... [Pg.59]

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... [Pg.253]

The presence or absence of the dioxolane protecting group in dienes dictates whether they participate in normal or inverse-electron-demand Diels-Alder reactions.257 The intramolecular inverse-electron-demand Diels-Alder cycloaddition of 1,2,4-triazines tethered with imidazoles produce tetrahydro-l,5-naphthyridines following the loss of N2 and CH3CN.258 The inverse-electron-demand Diels-Alder reaction of 4,6-dinitrobenzofuroxan (137) with ethyl vinyl ether yields two diastereoisomeric dihydrooxazine /V-oxide adducts (138) and (139) together with a bis(dihydrooxazine A -oxide) product (140) in die presence of excess ethyl vinyl ether (Scheme 52).259 The inverse-electron-demand Diels-Alder reaction of 2,4,6-tris(ethoxycarbonyl)-l,3,5-triazine with 5-aminopyrazoles provides a one-step synthesis of pyrazolo[3,4-djpyrimidines.260 The intermolecular inverse-electron-demand Diels-Alder reactions of trialkyl l,2,4-triazine-4,5,6-tricarboxylates with protected 2-aminoimidazole produced li/-imidazo[4,5-c]pyridines and die rearranged 3//-pyrido[3,2-[Pg.460]

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]

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). [Pg.561]

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. [Pg.512]

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. ... [Pg.161]

Although the tendency of benzofuroxan derivatives to interact with electron donors has been known since Drost s early report197 199 firm experimental evidence on the formation of Meisenheimer adducts was not reported until the 60s for the reaction of 4,6-dinitrobenzofuroxan with RO nucleophiles200 202 (Eq. 25). Information on benzofurazans became available even later with an NMR study by Terrier, Simonnin, and their co-workers.203... [Pg.417]

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]

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... [Pg.184]

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... [Pg.167]

Dinitrobenzofurazan 7-aminoderivatives have been obtained by the reaction of 4,6-dinitrobenzofuroxan with alkali metal salts of the corresponding formanyli-dines (Scheme 2.87) [527-529],... [Pg.119]

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]

In the absence of a leaving group, several well-defined reactions may still occur. The adducts (235) of 4,6-dinitrobenzofuroxan with hydroxide ion have long been known, and have received further study on account of their explosive properties the barium492 and potassium493 salts are the subjects... [Pg.333]

The kinetics and equilibria of the reaction of 4,6-dinitrobenzofuroxan with water (forming 235),494 496and of the cyclization of 7-(hydroxyethoxy)-4-nitrobenzofuroxan with alkali, in water and in dimethyl sulfoxide (Eq. II)497 have received detailed study. Proton NMR spectroscopy has shown that methoxide ions add more quickly to the 5-position of 7-methoxy-4-nitrobenzofuroxan, but the thermodynamic product is the 7,7-dimethoxy adduct (237) (Eq. 12).498 Methoxide adducts are also formed with 4-nitro-benzofuroxan.499 The impetus for much of this work was provided by the suggestion that antitumor and antileukemic properties which have been observed in some benzofuroxans might be connected with their ability to form Meisenheimer complexes of the types illustrated in this section.300,416,500... [Pg.334]

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]

Potassium salt of 7-hydroxylamino-4,6-dinitro-4,7-dihydrobenzofuroxan can be prepared in the same way as KDNBF. It is formed by the reaction of 4,6-dinitrobenzofuroxan with hydroxylamine in presence of a methanolic solution of potassium bicarbonate. The yield is nearly quantitative [48]. [Pg.175]


See other pages where 4.6- Dinitrobenzofuroxan reactions, with is mentioned: [Pg.284]    [Pg.292]    [Pg.305]    [Pg.251]    [Pg.251]    [Pg.232]    [Pg.439]    [Pg.113]    [Pg.568]    [Pg.576]    [Pg.578]    [Pg.203]    [Pg.365]    [Pg.293]    [Pg.252]    [Pg.425]    [Pg.427]    [Pg.691]    [Pg.577]    [Pg.26]    [Pg.184]    [Pg.135]    [Pg.158]    [Pg.523]   


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4.6- Dinitrobenzofuroxan reactions with nucleophiles

Dinitrobenzofuroxan

Dinitrobenzofuroxan, reactions

Dinitrobenzofuroxane

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