Reduction of nitroarenes

Nitroarene reductases catalyze the reduction of nitroarenes. They are flavoprotein (FMN) enzymes (Blehert et al. 1999) and are of two types  

Type 1 are 02-insensitive six-electron reductases that catalyze the sequential reduction of nitroarenes to nitroso, hydroxylamino, and amino arenes. They are encoded in E. coli by NfsA for the major enzyme and NfsB for the minor (Rau and Stolz 2003), and are also important in establishing resistance to nitrofuran drugs (Koziarz et al. 1998). 

Type 11 are 02-sensitive two-electron reductases that catalyze the reduction to ArN02 radicals that react with O2 to produce superoxide (Bryant and DeLuca 1991 Bryant et al. 1991). 

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Reduction of nitroarenes has been demonstrated in species of Clostridium and Eubacte-rium, and was associated with the reduction in the mutagenic activity of 1-nitropyrene, and... 

Scheme 2.5 Products formed in the transfer hydrogenation reduction of nitroarenes by complex 35...

The Bunce group disclosed a straightforward domino process for the construction of aryl-fused nitrogen heterocycles by employing a combination of a reduction and a Michael addition [20]. The transformation involves an initial Fe-mediated reduction of nitroarenes 7-38, furnishing an aniline which undergoes a subsequent... 

The reduction of nitroarenes to azoxy compounds ArN=N(0)Ar is promoted by bismuth trichloride/powdered zinc427. Aromatic amines are formed in excellent yields in the reduction of nitroarenes with BH3/NiCl2428 or nickel boride429. Acyl, ester, amide and cyano groups are not affected. Reaction of the nitro compounds RCH2N02 (R = Ph, Bz... 

In many respects the apparently analogous reduction of nitroarenes with triruthenium dodecacarbonyl under basic phase-transfer conditions is superior to that of the iron carbonyl-mediated reductions. However, the difference in the dependence of the two processes on the concentration of the aqueous sodium hydroxide and the pressure of the carbon monoxide suggests that they may proceed by different mechanisms. Although the iron-based system is most effective under dilute alkaline conditions in the absence of carbon monoxide, the use of 5M sodium hydroxide is critical for the ruthenium-based system, which also requires an atmosphere of carbon monoxide [11]. The ruthenium-based reduction has been extended to the... 

Selected examples of the ruthenium promoted reduction of nitroarenes... 

The mechanism and rate of reduction of nitroarenes by cluster rhodium/cobalt carbonyls under basic conditions and catalysed by dodecyltrimethylammonium chloride has been reported [13]. 

A more practical procedure for the reduction of nitroarenes to A-arylhydroxyl amines is the use of NaBH4 in the presence of a catalytic amount of tellurium. 

Phenyltellurol is another valuable reagent for the reduction of nitroarenes (and nitrocy-cloalkanes) to the corresponding amines. 

Sodium phenyl tellurolate is a milder reducing agent than phenyltellurol. The reduction of nitroarenes is therefore limited at the intermediate azoxy or azo compound stage, depending on the reaction temperature. The reagent is prepared in situ by treatment of diphenyl ditelluride with NaBH4 in ethanol in the presence of sodium hydroxide. Since the... 

Stilbenes, photocyclization of, 30, 1 StiUe reaction, 50, 1 Stobbe condensation, 6, 1 Substitution reactions using organocopper reagents, 22, 2 41, 2 Sugars, synthesis by glycosylation with sulfoxides and sulfinates, 64, 2 Sulfide reduction of nitroarenes, 20, 4 Sulfonation of aromatic hydrocarbons and aryl halides, 3, 4 Swem oxidation, 39, 3 53, 1... 

Zinc-copper couple, 20, 1 58, 1, 2 Zinin reduction of nitroarenes, 20, 4... 

The products of the reduction of nitroarenes possessing a second reducible group with various alcohols over MgO, donor acceptor ratio-6, HLSV-1... 

Ion-pairing effects may be crucial in determining the competition between radical and nonradical reactions. Recent investigations have shown that ion pairing accelerates the reduction of nitroarenes in alcoholic media.60 Therefore, the higher yields of substitution products often obtained in the absence of ion pairing are due, at least in some cases, not only to the promotion of substitution, but also to the depression of radical pathways. 

Reduction of nitroarenes (6, 281 9, 237). Ethanol-dichloroethane (1 1) is recommended as the solvent for reduction of nitroarenes to aminoarenes by hydrazine hydrate in combination with Raney nickel. Yields are nearly quantitative.1. 

Pentacarbonyliron has also been applied as catalyst for the reduction of nitroarenes by carbon monoxide and water to afford anilines [17, 83]. 

Recalling that arylamines are normally prepared by reduction of nitroarenes, we see that ethyl m-nitrophenyl ketone is a pivotal synthetic intermediate. It is prepared by nitration of ethyl phenyl ketone, which is analogous to nitration of acetophenone, shown in Section 12.16. The preparation of ethyl phenyl ketone by Friedel-Crafts acylation of benzene is shown in Section 12.7. 

In 2002, Brady reported a mechanistic study of the Sm(II)-mediated reduction of nitroarenes to anilines that provides a more detailed picture of nitro group reduction.41 The use of Sm[N(TMS)2]2 in place of Sml2 allowed a... 

Tsukinoki, T. Hirohisa, Tsuzuki. Organic Reaction in Water. Part 5. Novel Synthesis of Anilines by Zinc Metal-Mediated Chemoselective Reduction of Nitroarenes, Green Chem. 2001, 3, 37-38. 

Reduction of nitroarenes,l Nitrobenzenes substituted with chloro, methyl, or meth-oxy groups can be reduced to the corresponding anilines by formic acid and this ruth-enium(ll) complex in yields generally greater than 90%. Alcoholic solvents increase the... 

Reduction of nitroarenes (cf., 1, 440). Nitroarenes are reduced to amines in generally good yields by hydrazine hydrate with hydrated /8-iron(III) oxide, /3-FciO, H2O as catalyst. 

Reduction of nitroarenes. Sodium borohydride can reduce nitroarenes to the corresponding amines in 80-90% isolated yield in the presence of transition metal acctylacetonatcs, of which Cufacac), is the most effective. 

The reductive carbonylation of nitroarenes with transition metal catalysts is a very important process in industry, as the development of a phosgene-free method for preparing isocyanate is required. Ruthenium, rhodium, and palladium complex catalysts have all been well studied, and ruthenium catalysts have been shown to be both highly active and attractive. The reduction of nitroarene with CO in the presence of alcohol and amine gives urethanes and ureas [95], respectively, both of which can be easily converted into isocyanates [3,96]. 

Reduction of nitroarenes with CO in the presence of alkenes with allylic hydrogen gives allyl amines (Eq. 11.55) [104]. 

Selective reduction to hydroxylamine can be achieved in a variety of ways the most widely applicable systems utilize zinc and ammonium chloride in an aqueous or alcoholic medium. The overreduction to amines can be prevented by using a two-phase solvent system. Hydroxylamines have also been obtained from nitro compounds using molecular hydrogen and iridium catalysts. A rapid metal-catalyzed transfer reduction of aromatic nitroarenes to N-substituted hydroxylamines has also been developed the method employs palladium and rhodium on charcoal as catalyst and a variety of hydrogen donors such as cyclohexene, hydrazine, formic acid and phosphinic acid. The reduction of nitroarenes to arylhydroxyl-amines can also be achieved using hydrazine in the presence of Raney nickel or iron(III) oxide. ... 

The selective reduction of nitroarenes containing benzyl-protected phenolic groups without concomitant hydrogenolysis has also been achieved using hydrazine hydrate and Raney nickel. This procedure avoids strongly acidic conditions. The reaction is selective and a variety of (V-benzyl- and chloro-sub-stituted nitroarenes are reduced to the corresponding anilines without dehalogenation or debenzylation. 

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