Nitro compounds with nucleophiles

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. 

W. R. Bowmann, Reactivity of Substituted Nitro Compounds with Nucleophiles, Chem. Soc. Rev. 17, 283 (1988). 

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. ... 

Couplings of nitroalkyl radicals with nucleophiles such as CN-, N, N02, and other nitrogen nucleophiles provides a useful method for the preparation of nitro compounds with such groups at the a-position.49 65 The alkylation of nitromethane with trialkylborane is possible by electrolysis, in which alkyl radicals may be involved (Eq. 5.46).66... 

In 1982, a new reaction was reported by Tamura and Ono namely, allylic nitro compounds undergo replacement of the nitro group by various nucleophiles in the presence of a palladium (0) catalyst.17a b 18a b The details of these reactions are discussed in Ref. 2b here, only some typical examples are presented. Carbon, sulfur, nitrogen, and phosphorous centered nucleophiles replace the nitro groups at the allylic positions. The reaction of allylic nitro compounds with triphenylphosphine is applied to the highly stereoselective olefination of aldehydes (Eqs. 7.15-7.18).19... 

Aromatic nitro compounds undergo nucleophilic aromatic substitutions with various nucleophiles. In 1991 Terrier s book covered (1) SNAr reactions, mechanistic aspects (2) structure and reactivity of anionic o-complexes (3) synthetic aspects of intermolecular SNAr substitutions (4) intramolecular SNAr reactions (5) vicarious nucleophilic substitutions of hydrogen (VNS) (6) nucleophilic aromatic photo-substitutions and (7) radical nucleophilic aromatic substitutions. This chapter describes the recent development in synthetic application of SNAr and especially VNS. The environmentally friendly chemical processes are highly required in modem chemical industry. VNS reaction is an ideal process to introduce functional groups into aromatic rings because hydrogen can be substituted by nucleophiles without the need of metal catalysts. 

The first stage of the synthesis involves the interaction of a nitro compound with sodium sulfide. When used alone, sodium sulfide is only slightly effective The reactions proceed slowly and the yields of mercaptanes are small. If elemental sulfur is added, the conversion accelerates markedly and the yield increases to 75-80%. The promoting effect of elemental sulfur can be easily explained by the radical-chain mechanism. The reaction starts with one-electron transfer from the nucleophile to the nitro compound further conversions resemble other chain ion-radical substitutions. 

The oxidation of nitrobenzene to o- nitrophenol (with traces of the p- isomer) when mixed with dry sodium hydroxide, and slightly heated, may be another example of the oxidation of nitro compounds by nucleophilic substitution (Wohl [46]) ... 

Action of bases in nucleophilic reactions of nitro compounds Action of Grignard reagent on nitro aimpounds Reaction of aromatic nitro compounds with diazomethane... 

Recently Bartoli and co-workers [85-87] have published a number of papers dedicated to the systematic study of the reaction of aromatic nitro compounds with Grignard reagent. They confirmed the nucleophilic character of the alkylation of the ring. They also found that under their experimental conditions the nitro group was reduced to the nitroso group (17) ... 

The reactions of nitro compounds with bases are nucleophilic reactions and recently have received much attention. Numerous monographs include chapters on nucleophilic substitution of nitro compounds and review articles have been published. Such are the excellent reviews by de Boer and Dirkx [9], Hall and Poranski [10]. References in [9] are brought up to 1966, and it seems appropriate to complete the list of review articles by mentioning the later review papers Chains [11], Buncel and co-workers [12], Miller (13),Pietra [14], Buck [IS], Crampton [16], Strauss [17], Bemasconi [18], Sekiguchi and Yuki [19],... 

Several methods exist for the synthesis of substituted 3-phenyl 1,2-benzisoxazoles or hetero-benzisoxazoles varying from heating of substituted benzophenone azides (Example 1), triethyl phosphite reduction of ortho-nitro benzophenone or heterophenone compounds (Example 2), even to nucleophilic substitution of nitro compounds with aryl acetonitriles (Example 3). °... 

Kinetic profiles of several base-catalyzed cycloaddition—condensation reactions of activated primary nitro compounds with dipolarophiles to isoxa-zolines (Machetti-De Sarlo reaction) were studied in both H2O and CHCI3 (13CEJ665). The copper-catalyzed intramolecular version of the same reaction was applied to the synthesis of tricyclic isoxazoline 39 starting from nitro derivative 38. Nucleophilic fragmentation of 39 afrbrded clean 40 that is a key intermediate for the synthesis of racemic tetrodotoxin (13JOC11901). 

Step (Scheme 1.220) [306]. The treatment of nitro compounds with Ag20, DBU, and iodine resulted in bicyclic cyclopropanes 470 and 471 in good yields. The stereoselectivity was generally high. The stereoselectivity depended on the size of the formed ring. The precursors 469 were readily prepared by the conjugate addition of allylic or homoallylic nucleophiles to nitroalkenes. A similar cyclo-propanation has also been reported [307]. 

Allylic nitro compounds form rr-allylpalladium complexes by displacement of the nitro group and react with nucleophiles, and allylation with the tertiary nitro compound 202 takes place at the more substituted side without rearrangement to give 203[8,9,128]. 

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

Nitro substituted aromatic compounds that do not bear halide leaving groups react with nucleophiles according to the equation... 

I itro-DisplacementPolymerization. The facile nucleophilic displacement of a nitro group on a phthalimide by an oxyanion has been used to prepare polyetherimides by heating bisphenoxides with bisnitrophthalimides (91). For example with 4,4 -dinitro monomers, a polymer with the Ultem backbone is prepared as follows (92). Because of the high reactivity of the nitro phthalimides, the polymerkation can be carried out at temperatures below 75°C. Relative reactivities are nitro compounds over halogens, Ai-aryl imides over A/-alkyl imides, and 3-substituents over 4-substituents. Solvents are usually dipolar aprotic Hquids such as dimethyl sulfoxide, and sometimes an aromatic Hquid is used, in addition. 

Nucleophilic aromatic substitutions involving loss of hydrogen are known. The reaction usually occurs with oxidation of the intermediate either intramoleculady or by an added oxidizing agent such as air or iodine. A noteworthy example is the formation of 6-methoxy-2-nitrobenzonitrile from reaction of 1,3-dinitrobenzene with a methanol solution of potassium cyanide. In this reaction it appears that the nitro compound itself functions as the oxidizing agent (10). 

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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