Aromatic nitro group, reduction

The resin-bound perfluoroalkylsulfonyl linker is compatible with many common solid-phase reactions, such as tin dichloride-mediated aromatic nitro group reduction, trifluoroacetic acid-mediated tBoc deprotection, reductive amination reactions, acylation, and sulfonation. It is possible to perform several sequential synthetic reactions on the nonflate resin so that multistep syntheses can be carried out. The solid-phase approach provides an operationally simple, inexpensive, and general protocol for the cleavage... 

Juchau MR, Krasner J, Yoffe SJ. 1970. Model systems for aromatic nitro group reduction-relationships to tissue catalyzed reagents. Biochem Pharmacol 19 443-455. 

There is no problem of chemoselectivity here it is not possible to reduce the aliphatic NO group in (10) without reducing the aromatic NO group too. This is easily solved by introducing the aromatic nitro group after the reduction. 

A Reductions of Heterocyclic N-Oxides and Aromatic Nitro Groups 1165... 

Electrochemically generated nickel is very selective for the reduction of aromatic nitro compounds into anilines, in which alkenyl, alkynyl, halo, cyano, formyl, and benzyloxy groups are not affected.84 Sodium sulfide has been used for the selective reduction of aromatic nitro group in the presence of aliphatic nitro groups (Eq. 6.44).85... 

Reductions with zinc are carried out in aqueous [160 as well as anhydrous solvents [163 and at different pHs of the medium. The choice of the reaction conditions is very important since entirely different results may be obtained under different conditions. While reduction of aromatic nitro groups in alkali hydroxides or aqueous ammonia gives hydrazo compounds, reduction in aqueous ammonium chloride gives hydroxylamines, and reduction in acidic medium amines (p. 73). Of organic solvents the most efficient seem to be dimethyl formamide [164 and acetic anhydride [755]. However, alcohols have... 

Reduction of aromatic nitro group takes preference to the reduction of the aromatic ring. Under certain conditions, however, even the benzene ring was reduced. Hydrogenation of nitrobenzene over platinum oxide or rhodium-platinum oxide in ethanol yielded aniline while in acetic acid cyclohexylamine was produced [55]. Heating of nitrobenzene with formic acid in the presence of copper at 200° gave a 100% yield of aniline, whereas similar treatment in the presence of nickel afforded 67% of cyclohexylamine [71]. 

A very reliable reagent for reductions of aromatic nitro groups in the presence of sensitive functions is iron, which does not affect carbon-carbon double bonds [555]. 

Methylcryptaustoline iodide (14) was synthesized from phenylacetic acid 47 by Elliott (39) as shown in Scheme 7. Nitration of 47 to the 6-nitro compound 48 and reduction with sodium borohydride afforded lactone 49. Reduction of the aromatic nitro group with iron powder in acetic acid gave ami-nolactone 50, which was converted to tetracyclic lactam 51 with trifluoroacetic acid in dichloromethane. Reduction of the lactam by a borane-THF complex followed by treatment with methyl iodide afforded ( )-0-methylcryptaustoline iodide (14). 

Since most anilines are derived from nitro intermediates the reduction of the aromatic nitro group followed by cyclization of the aniline in situ has offered a direct approach to the synthesis of quinolines. The ort/io-nitro cinnamic acid derivatives 28 undergo cyclization, where R corresponds to R , respectively, when treated with zinc in near-critical water at 250 °C... 

The reduction of aromatic nitro groups by use of electro-generated titanium(III) has also been investigated very intensively, especially in India. Thus, aniline derivatives are generated in high yield Evidently this method has some... 

In the following we will try to illustrate these general points by discussing two specific types of redox reactions the reduction of aromatic nitro groups (Eq. 14-9) and the reductive dehalogenation of polyhalogenated Cr and C2-compounds (Eqs. 14-6 to 14-8). These two cases represent two very different types of reactions. In the first case, the transfer of the first electron is reversible, whereas in the second case, it is typically irreversible and involves the breaking of a bond. In the latter case, therefore, one speaks of a dissociative electron transfer. Furthermore, compounds... 

A combination of iron(III) salts with solid-supported hydrazine hydrate (preabsorbed on AI2O3) were successfully used in reductions of aromatic nitro groups (Scheme 4.33). The nature of the solid support plays a crucial role in this reaction and alumina was found to be most effective. In the absence of a solid support, the reaction... 

Aromatic amines are readily prepared by the reduction of aromatic nitro groups by Fe/HCl or Sn/HCl or by catalytic hydrogenation. 

The resin-bound phenylene diamine intermediates 3 are then generated by nitro group reduction with tin(II) chloride in NMP and cyclization/ aromatization with a wide variety of aldehydes gave the resin-bound benzimidazole intermediates 4. The treatment of this intermediate with 50% TFA/DCM liberates the substituted 3-(benzoimidazol-l-yl)-propionic acid derivative 4a. Analysis of this intermediate by HPLC and LC-MS gave a measure of the purity of the resin-bound product and enabled the optimization of conditions for the incorporation of the Rl-nitroarenes and R2-aldehydes by an iterative process. 

Reduction of an Aromatic Nitro Group on Solid Phase (Fig. 15).45 Resin 81 (1 g, 0.47 mmol/g) is suspended in 20 ml of a 1.5 M solution of SnCl2-2H20 in DMF. The mixture is shaken for 12-24 h and filtered. The resin is washed with MeOH, CH2C12, DMF, dioxane, and Et20 and dried in vacuo to obtain (82). 

Reduction of aromatic nitro groups occurs in three steps, via nitroso and hydroxylamine intermediates, to the amine. The amine can go on to form polymeric residues by a mechanism analogous to that for oxidative coupling of phenols, as in Equation 2. Abiotic nitro reduction is well documented for pesticides that contain aromatic nitro groups, such as the phosphorothioate esters methyl and ethyl parathion (22, 30-33). 

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