Nitrobenzene, reaction with unsaturated

Carbon dioxide radical anions, C02 , are commonly used in aqueous chemistry as a reducing agent for metalloporphyrins or as intermediate in the formation of superoxide anion. COf has been reported to undergo efficient electron transfer reactions with methyl violo-gen, quinones, alkyl halides, fumarates, nitro and nitrosobenzenes and chlorinated benzaldehydes. With nitrobenzenes and chlorinated benzaldehydes, electron attachment occurs on the nitro and aldehyde groups, respectively. CO2 radicals have also been reported to add to some unsaturated compounds such as acrylamide and pyridin-3-ol. Efficient hydrogen abstraction from mercaptobenzenes have also been reported. 

For the formation of 45, nitrobenzene would be reduced to aniline by CO/H2O (see Chapter 4.2.). By aldol condensation, an a,p-unsaturated aldehyde is formed. Michael addition of aniline to the unsaturated aldehyde followed by ring closure with dehydration would form 1,2-dihydroquinoline. Oxidation of this last product by nitrobenzene would yield 45. This sequence of reactions is similar to what proposed in Scheme 15. For the formation of 46, an intermediate nitrene was suggested (Scheme 16). Addition of the nitrene to the aldehyde would give an oxaziridine and, correspondingly, an isomeric nitrone. The nitrone would then be reduced by CO to the Schiff base and this, in turn, would be reduced to the amine. Final reaction with one more molecule of aldehyde would lead to 46. Some previously made comments on the formation of Schiff bases from nitroarenes and aldehydes vide supra and Chapter 4.5.) also apply to the first part of this scheme. 

The chemistry of indium metal is the subject of current investigation, especially since the reactions induced by it can be performed in aqueous solution.15 The selective reductions of ethyl 4-nitrobenzoate (entry 1), 2-nitrobenzyl alcohol (entry 2), l-bromo-4-nitrobenzene (entry 3), 4-nitrocinnamyl alcohol (entry 4), 4-nitrobenzonitrile (entry 5), 4-nitrobenzamide (entry 6), 4-nitroanisole (entry 7), and 2-nitrofluorenone (entry 8) with indium metal in the presence of ammonium chloride using aqueous ethanol were performed and the corresponding amines were produced in good yield. These results indicate a useful selectivity in the reduction procedure. For example, ester, nitrile, bromo, amide, benzylic ketone, benzylic alcohol, aromatic ether, and unsaturated bonds remained unaffected during this transformation. Many of the previous methods produce a mixture of compounds. Other metals like zinc, tin, and iron usually require acid-catalysts for the activation process, with resultant problems of waste disposal. 

The photochemical action of nitrobenzene on unsaturated compounds in sunlight is a field already investigated by Vechiotti and Zanetti.295 Recently, Buchi and Ayer32 have evaluated the reaction of nitrobenzene with olefins as a possible synthetic route to the heterocyclic class of compounds, 1,3,2-dioxazolidines (CXLVI). Photoexcited... 

Protonation of glycerol 6.4 catalyses dehydration via secondary carbonium ion 6.5 to give enol 6.6. Acid catalysed elimination of a second water molecule affords acrolein 6.7. Thus glycerol acts essentially as a protected form of acrolein, slowly releasing this unstable a,p unsaturated aldehyde into the reaction medium. Better yields are realised with this approach than if acrolein itself is present from the start. The reaction proceeds with a Michael addition of aniline 6.3 to acrolein, producing saturated aldehyde 6.8 which cyclises via an aromatic substitution reaction to alcohol 6.9. Acid-catalysed dehydration to 6.10 then oxidation yields quinoline 6.1. Nitrobenzene can be used as a mild oxidant, as can iodine and ferric salts. 

The synthetic potential of these catalysts has been investigated in Heck-type coupling reactions treatment of l-bromo-4-nitrobenzene with n-butyl acrylate in isopropyl alcohol in the presence of 2.5 mol% of catalyst and tetrabutylammonium acetate afforded the unsaturated ester in an excellent... 

It has been stated that the aromatic compounds differ markedly from the paraffins and the unsaturated hydrocarbons related to ethylene and acetylene. The reactions which take place when benzene and its derivatives are treated with nitric acid, sulphuric acid, or oxidizing agents are characteristic of this group of compounds. Only the higher paraffins react with nitric acid, and in the case of these compounds reaction results to but a slight degree and only after heating for many hours (26). The aromatic hydrocarbons and their substitution-products form well characterized compounds when treated with nitric acid. When benzene is warmed with concentrated nitric acid nitrobenzene is formed —... 

This reaction was initially reported by Doebner and von Miller in 1881 as a modification of the original Skraup Reaction, and it was subsequently modified by Beyer in 1886 It is an acidic condensation between primary aromatic amines (e.g., anilines) and Q ,j8-unsaturated carbonyl compounds (mostly o ,y3-unsaturated aldehydes) to give 2,3-disubstituted quinolines. Therefore, this reaction is generally known as the Doebner-Miller reaction, or Doebner-Miller synthesis." In addition, this reaction is also referred to as the Doebner-von Miller quinoline synthesis, Skraup-Doebner-von Miller reaction, Skraup-Doebner-von Miller quinoline synthesis, Doebner-Miller condensation, and Doebner-Miller Quinaldine Synthesis. For comparison, the modification from Beyer, known as the Beyer method for quinoline, is an acidic condensation between anilines and Q ,j8-unsaturated carbonyl compounds generated in situ from aldehyde or aldehyde and methyl ketone to afford 2,4-disubstituted quinolines." The optimal condition of this reaction is to heat the mixture of aniline/aldehyde (1 2) at 100°C for 6 h with hydrochloric acid and zinc chloride in addition, an oxidizing reagent is also needed in this reaction, such as nitrobenzene. However, it has been reported that A -alkylanilines are also formed in this reaction. The nature and... 

Alternatively, the oxidation may occur by coupling to a suitable reactant. In 1997, Miyashita explored the scope of oxidative aroylations with nitrobenzene (Scheme ll.lO)." With the same oxidative reagent, nitrobenzene, benzoin reactions had already been developed back in 1982 using cyanide or thiamine. The combination of an aldehyde and nitrosobenzene, in the presence of an NHC, led to the formation of 7V-phenyl hydroxamic acids in good yields. These can be further converted into hydroxamic esters via a one pot reaction in the presence of a second (o,p-unsaturated) aldehyde. Furthermore, the oxidative coupling of aldehydes with carbodiimides in air allowed access to Af-acyl urea derivatives with IMes HCl 19 as the NHC precursor. Related thioesterifications reactions have also been reported using... 

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