Arylation of Nitro Compounds

Arylations of nitro compounds can be achieved by aromatic nucleophilic substitution using aromatic nitro compounds, as discussed in Chapter 9.100 Komblum and coworkers reported displacement of the nitro group of nitrobenzenes by the anion of nitroalkanes. The reactions are usually carried out in dipolar aprotic solvents such as DMSO or HMPA, and nitroaromatic rings are substituted by a variety of electron-withdrawing groups (see Eq. 5.63).101 

There are many cine substitution reactions of aromatic nitro compounds using various nucleophiles.100 In this chapter, the cine-substitution reactions using the anion of nitroalkanes 

In general, heterocyclic nitro compounds undergo cine substitution reactions more readily than nitrobenzenes. For example, the reaction of 5-acyl- or 5-alkoxycarbonyl-2-nitrofurans with the anion of nitroalkanes gives cine substitution products in excellent yields (Eq. 5.66).104 

The reaction of l,2-dimethyl-5-nitroimidazole with 2-nitropropane anion gives the new highly branched imidazole derivative, which is formed via cine-substitution and SRN I substitution (Eq. 5.67).slb 

Barton and coworkers have explored the arylation of various nucleophiles including nitroalkanes using bismuth reagents.105 Reaction of 2-nitropropane with triphenylbismuth carbonate gives 2-nitro-2-phenylpropane in 80% yield.106 Recently, this arylation has been used for the synthesis of unusual amino acids. Arylation of a-nitro esters with triphenylbismuth dichloride followed by reduction gives unique a-amino acids (Eq. 5.68).107 

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Intramolecular cyclization using palladium-catalyzed arylation of nitro compounds has been reported recently (Eq. 5.71).114... 

Aliphatic nitro compounds can be arylated using appropriate catalyst systems. For example, the reaction of nitroethane using a bulky phosphine affords the corresponding monoarylated product with good selectivity and yield (Eq. 32) [15]. The intramolecular version of a-arylation of nitro compounds has also been reported (Eq. 33) [59]. 

Organic nitro compounds, RNO2, can be reduced to amines. The R may be either alkyl or aryl. Aromatic nitro compounds are easy to prepare and reduce. Their preparation utilizes a mixture of nitric acid and sulfuric acid to nitrate the aromatic ring. (However, multiple nitrations may occur, potentially causing problems.) The nitro group can be reduced with a... 

Tertiary alkyl primary amines can be oxidized to nitro compounds in excellent yields with KMn04.39S This type of nitro compound is not easily prepared in other ways. All classes of primary amine (including primary, secondary, and tertiary alkyl as well as aryl) are oxidized to nitro compounds in high yields with dimethyldioxirane.399 Other reagents that oxidize various types of primary amines to nitro compounds are dry ozone,4,111 various peracids,401 including peracetic and peroxytrifluoroacetic acids, f-butyl hydroperoxide in the presence of certain molybdenum and vanadium compounds,402 F7-H20-MeCN,41123 and sodium perborate.403... 

The [Ru(bpy)3] photocatalyst was also applied in the following novel visible-light driven processes (i) synthesis of indazolo[2,3-a]quinoline derivatives from 2-(2-nitrophenyl)-l,2,3,4-tetra-hydroquinolines (ii) azido- and amino-trifluoromethylation of alkenes (iii) reduction of nitro compounds to oximes (iv) generation of aryl radicals by visible-light photocatalytic reduction of sulfonium salts. ... 

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). °... 

Except for amines (Experiment 52G), which are easily detected by their solubility behavior, all compoimds issued in this experiment will contain heteroelements (N, S, Cl, Br, or I) only as secondary functional groups. These will be subsidiary to some other important functional group. Thus, no alkyl or aryl halides, nitro compounds, thiols, or thioethers will be issued. However, some of the unknowns may contain a halogen or a nitro group. Less frequently, they may contain a sulfur atom or a cyano group. 

A number of studies of the important (non-phosgene) route to aryl isocyanates via carbonylation of nitro compounds have appeared. In a comparative study of Rh(I), Ir(I), Pd(I) and Pd(II) catalysts, Bu,N+[RhX2(CO)2] (X Cl, Br, I) was most effective giving 83-89% PhNCO with 100% PhN02 conversion at 125 C under 80 atm CO pressure . The kinetics of carbonylation by [PdCl2py2l at 170-230 C and 23-94 atm CO pressure are first order in p[CO] and catalyst and zero order in PhNOj . The reductive N-carbonylation of nitroarenes to the carbamates is catalysed by tPtCl2 (PPh3 >2] in ethanol, promoted by Lewis acids (SnCli,... 

Keywords Aryl/heteroaryl nitro compounds, Zn dust, ammonium chloride (NH4CI), TPGS-750-M (surfactant), water, room temperature, chemoselective recustion of nitro group, amino derivatives... 

Dilute sodium hydroxide solution. Carboxylic acids (RCOOH), sulphonic acids (RSO3H), phenols (ArOH), thiophenols (ArSH), mer-captans (RSH), imides (RCONHCOR), aryl sulphonamides (AxSOjNHj), arylsulphonyl derivatives of primary amines (AxSOjNHR), oximes (RCH=NOH), primary and secondary nitro compounds (RCH=NOOH and RjC=NOOH-oci forms), and some enols (e.g., of 1 3-diketones... 

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