Nitroarenes selective

Carbo- and heterocyclic nitroarenes react with anions of tert-butyl and cumyl hydroperoxides in the presence of strong bases to form substituted o- and p-nitrophenols. Regiochemistry of the hydroxylation can be controlled to a substantial extent by selection of proper conditions (Eq. 9.52).85... 

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

The anodic chlorination in some cases allows one to achieve better regioselec-tivities than chemical alternatives (p/o ratio of chlorotoluene in chlorination of toluene anodic 2.2, chemical alternative 0.5-1.0) [215]. Anodic oxidation of iodine in trimethyl orthoformate afforded a positive iodine species, which led to a more selective aromatic iodination than known methods ]216]. Aryliodination is achieved in good yield, when an aryhodide is oxidized in HOAc, 25% AC2O, 5% H2SO4 in the presence of an arene ]217, 218]. Alkyl nitroaromatic compounds, nitroaromatic ketones, and nitroanihnes are prepared in good yields and regioselectivity by addition of the corresponding nucleophile to a nitroarene and subsequent anodic oxidation of the a-complex (Table 13, number 11) ]219, 220]. 

The vicarious nucleophilic substimtion of carbo- and hetero-cyclic nitroarene hydrogen by a hydroxyl group, on reaction with silylhydroperoxide anions, has been shown to proceed via nucleophilic addition of ROO followed by base induced elimination of ROH by an ii2-type mechanism the required orientation of the hydroxylation can be controlled by the conditions selected. ... 

TABLE 10.33 Concentrations of Selected Nitroarenes in Extracts of Diesel Particulate POM b... 

Magnesium oxide exhibited high activity and high selectivity in the hydrogen transfer from alcohols to studied nitroarenes. Because of the limited space of the paper the complete amine yield - temperature dependence was shown only for nitrobenzene reduction (Table 1). However, also for other reactants the yield of the aminic product increased continously between the values obtained at the lowest (350°C) and the highest (450°C) reaction temperatures. Below 350°C the complete lack of activity of MgO in the studied transformation was noted. The same was observed by us earlier (ref. 2) in the case the catalytic transfer reduction of other functional groups. 

The alkylation reaction is limited to nitro-substituted arenes and heteroarenes and is highly chemoselec-tive nucleophilic displacement of activated halogens, including fluorine, was not observed. The regio-selectivity is determined by the bulkiness of the silicon reagent. With unhindered silyl derivatives a strong preference for ortho addition was observed, as in the example of equation (6). With bulkier reagents attack took place exclusively at the para position (Scheme 1). The success of this reaction, which could not be reproduced with alkali enolates, was attributed at least in part to the essentially nonbasic reaction conditions under which side processes due to base-induced reactions of nitroarenes can be effectively eliminated.12... 

NaOCl converts the alkyl nitronate adducts formed between nitroarenes and Grignard reagents, to alkyl chloroarenes814. tert-Butyl hypochlorite selectively chlorinates benzal-doximes to afford benzohydroximoyl chlorides8 5. 

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. 

Sodium borohydride reduces disulfides to thiols, which can then be used to reduce nitro groups. Based on the redox properties of 1,2-dithiolane, lipoamide (17) was used for the selective reduction of mono-substituted nitrobenzenes to the corresponding anilines. Lipoamide (17) can also be immobilized on hydrophilic polymers such as polyvinylamine, polyethyleneimine and chitosan. These polymeric reducing catalysts can be recycled and are easy to separate from the reaction mixture. The system has been used to reduce nitroarenes to anilines. ... 

The iron cluster [Fe4S4(SPh)4] catalyzes the reduction of nitroarenes to arylamines. " A less hydridic nucleophile [HFe(CO)4] has also found application as a selective reducing agent for nitroarenes." Although [HFe(CO)4]"] is known to reduce aldehydes, ketones and acid halides," in THF solvent with tri-fluoroacetic acid, it selectively reduces nitrobenzenes to anilines in the presence of aldehyde and acid halide groups. 

Future trends in reduction of substituted nitrobenzenes will probably be based on novel catalysts. Homogenous transition metal (ruthenium and rhodium) catalysts offer routes to chemospecific reduction of aromatic nitro groups16. Novel catalytic methods involving combinatorial chemistry may offer pathways to new industrial hydrogenation processes, where selective reduction is desired. A number of solution- and solid-phase C /Mo0 redox couple reductions of substituted nitroarenes to the corresponding anilines have been proposed17. 

In the presence of molten SbCls, anthracene and naphthacene are selectively hydrogenated by tetralin to give 9,10-dihydroanthracene and 5,12-dihydronaphtha-cene, respectively [31]. Both SbCls-Al and SbCls-Zn binary systems reduce a variety of aldehydes to the corresponding primary alcohols in DMF-H2O (Scheme 14.10) [32]. In the presence of a catalytic amount of SbCl3, acetophenones are reduced to 1-arylethanols by an electrochemical method [33]. Nitroarenes are reduced by Sb-NaBH4 in MeOH [34], and by Sb(.l, -Nal H4 in EtOH [35] to afford N-arylhydroxylamines (Scheme 14.11) and anilines (Scheme 14.12), respectively. 

Reactions of nitroarenes with vinylmagnesium halides give indoles (the Bartoli reaction).607 Site selectivity problems may be avoided by temporarily installing a bromine ortho to the nitro group (Eq. 187).608... 

BINAS, 38) catalyzed the selective reduction of nitroarenes to anilines at 100°C under 120 bar CO [149]. 

A similarly selective reduction of nitroarenes was achieved under WGS conditions by using [ Ru3(CO)12] in the presence of certain amines, such as diisopropylamine, piperidine, dibutylamine, and triethylamine [146]. Importantly, the latter reaction yielded no unwanted H2 as by-product from a concomitant WGS reaction. 

Other peroxidases such as HRP or CPO were also able to perform such reactions. Another approach to the production of nitroarenes with peroxidases is based on the CPO (or bromoperoxidase)-catalyzed oxidation of arylamines. Table 16.3-10 gives a selection of peroxidase-catalyzed conversions of aniline derivatives to corresponding nitroarenes. 

Associated with some metals (Al, Fe, Zn), BiCl3 gives Bi(0) which is a catalyst for the allylation of aldehydes and amines (ref. 35), and for the reduction of aromatic nitro compounds to azoxy compounds (ref. 36). When associated with sodium borohydride, BiCl3 gives an efficient system for the selective reduction of nitroarenes and azomethines (ref. 37). 

Hydrogenation and dehydrogenation. Supported on carbon in a nanofiber form Pt catalyzes selective hydrogenation of nitroarenes to give arylamines in the presence of many other functional groups. ... 

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