Nitro reactions with nucleophiles

The most common types of aryl halides in nucleophilic aromatic substitutions are those that bear- o- or p-nitro substituents. Among other classes of reactive aryl halides, a few merit special consideration. One class includes highly fluorinated aromatic compounds such as hexafluorobenzene, which undergoes substitution of one of its fluorines on reaction with nucleophiles such as sodium methoxide. 

Bowman has surveyed the reactions of cx-substituted aliphatic nitro compounds with nucleophiles, which undergo either S l substitution or polar reaction (Scheme 5.16).118 The reactions between a wide variety of nucleophiles and BrCH2N02 are shown in Scheme 5.17.119a b All the thiolates, PhS02 and I attack Br to liberate the anion of nitromethane. The hard nucleophiles, MeO , OH, and BH4 attack the hard H+ electrophilic center. Phosphorous nucleophiles attackthe oxygen electrophilic center, and only Me2S attacks the carbon electrophilic center. 

Reactions of aliphatic nitro compounds with nucleophiles. 610... 

Reactions of aliphatic nitro compounds with nucleophiles have been reviewed442-444. The oxidative reaction of nitronate anions, e.g. 410, with thiocyanate anions to yield thiocyanates 411 proceeds by a radical radical-anion chain mechanism SrnI (equation 133). Analogous replacements by azide, benzenesulphinate and 4-chlorobenzenethiolate have been reported445. 

Substituted quinoxalines undergo unusual reactions with nucleophiles. Thus, 2,3-diphenyl-6-nitroquinoxaline (67) with potassium cyanide undergoes substitution in the 5-position, with simultaneous nucleophilic displacement of the 6-nitro group by the methanol solvent to give compound 68 (52%) 5-aminoisoxazolo[4,3-/]quinoxaline (69) is also obtained (35%). The structure of the product 68 was proved by an unambiguous synthesis.85... 

Many of the studies purporting to show nucleophilic attack upon co-ordinated heterocyclic ligands have been performed with complexes of 5-nitro-l,10-phenanthro-line, 8.20. Unfortunately, this ligand proves to be a less than optimal choice, as nitroalke-nes undergo facile reactions with nucleophiles and, in contrast to simple pyridines, the free ligand reacts with hydroxide ion. Hydroxide ion and other nucleophiles react with 8.20 at the 6-position to give the stabilised anion 8.21 (Fig. 8-20). It is almost certain that the majority of the reactions of 5-nitro-l,10-phenanthroline complexes with hydroxide... 

In the reaction with nucleophiles, halobenzenes with electron-withdrawing substituents such as nitro group in ortho or para (or both) positions activate the halogens for nucleophilic displacement. Which halogen is replaced more easily, chlorine or fluorine Explain why. 

Huonne in nitro derivatives of benzene shows a greater reactivity than chlorine in nucleophilic reactions (3). In view of this attention was paid to 1,3.5-trinuorotrinitrobenzcnc and its reaction with nucleophiles 31. 

In the dinitrobenzenecarboxamide, CB1954 or the quinones AZQ/BZQ (Figure 1, 12, 1 or 2 respectively), the aziridine moiety is deactivated by the electron-withdrawing nitro substituents or the electron-deficient quinone system respectively. However, on reduction the p Ta of the aziridine nitrogen increases, activating the site towards reaction with nucleophiles. 

Also Kuhn and Olah [21 nitrated 2,4-dinitronuorobenzenc with NOa HSO4 in 100% sulphuric acid at 120 C for 12 hours and obtained piciyl fluoride with the yield of 40% Eluonno in nitro derivatives of benzene shows a greater reactivity than chlorine in nucleophilic icdciioris [3). in view of ih.s aitcni.on was paid to 1,3.5-lrinuoroiriiiitroberizenc and its reaction with nucleophiles 13]. 

Reactions with Nucleophiles. As might be expected biphenylene does not react readily with nucleophiles. However the presence of a nitro-group may enable nucleophilic attack, and 2-nitrobiphenylene has been aminated at the 3-position [169] ... 

AUyUc nitro compounds react with Pd(0) species to form 7r-allylpalladium complexes, which undergo reaction with nucleophiles to give substitution products. l-(Nitroalkyl)-cycloalkenes react with dimethyl sodiomalonate in DMF in the presence of Pd(PPh3)4 catalyst to give alkylated product regioselectively (Scheme... 

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. ... 

Radical intermediates are involved in reactions of a-nitro-sulphones with nucleophiles, leading to products from which the sulphone grouping has been displaced. A useful method of synthesis of 1,2-dinitroalkanes emerges from... 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Alkoxyl tion. The nucleophilic replacement of an aromatic halogen atom by an alkoxy group is an important process, especially for production of methoxy-containing iatermediates. Alkoxylation is preferred to alkylation of the phenol wherever possible, and typically iavolves the iateraction of a chloro compound, activated by a nitro group, with the appropriate alcohol ia the presence of alkaU. Careful control of alkaU concentration and temperature are essential, and formation of by-product azoxy compounds is avoided by passiag air through the reaction mixture (21). 

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