Recent progress in transition metal catalyzed cross coupling of nitroarenes

The recent development in transition metal catalyzed cross coupling of nitroarenes was highlighted. And nitroarenes were efficient electrophilic coupling partners for constructing C–O, C–S, C—C and C–N bonds.     

Application of capillary gas chromatography to environmental analysis

Routine analytical methods for benzo[a]pyrene and nitroarenes in airborne particulates are presented. Benzo[a]pyrene in airborne particulates was easily analyzed by a capillary GC/NCIMS. Analysis time was about 10 min and analytical values obtained by this method agreed well with those by HPLC/spectrofluorometry. Nineteen nitroarenes were analyzed by capillary GC/FTD following a simple clean-up procedure. Fifteen out of 19 nitroarenes analyzed were mutagenic for Salmonella typhimurium TA100 and TA98, and 4 nitroarenes were carcinogenic to experimental animals.     

硝基芳烃直接氨化的新方法

评述了硝基芳烃直接氨化的几种新方法,主要是芳香亲核氢取代(NASH)反应,Vicarious亲核氢取代(VNS)反应以及由羟氨或烷氧基氨引起的直接氨化反应等。对每种反应的机理(或模式)也作了介绍。     

2-(N-Hydroxylamino) sulfone synthesis by indium-iodine-triggered aza-Michael type addition of nitroarenes to vinyl sulfones

One-pot reduction-triggered 1,4-addition reaction of various nitroarenes to the α,β-unsaturated sulfones was investigated. In the presence of indium/iodine in MeOH at room temperature, nitroarenes reduced in situ reacted with vinyl sulfones and produced β-(N-hydroxylamino) sulfones in good yields.     

A Reusable Co Catalyst for the Selective Hydrogenation of Functionalized Nitroarenes and the Direct Synthesis of Imines and Benzimidazoles from Nitroarenes and Aldehydes

The use of abundantly available transition metals in reactions that have been preferentially mediated by rare noble metals, for example, hydrogenations, is a desirable aim in catalysis and an attractive strategy for element conservation. The observation of novel selectivity patterns with such inexpensive metal catalysts is especially appealing. Herein, we report a novel, robust, and reusable cobalt catalyst that permits the selective hydrogenation of nitroarenes in the presence of highly hydrogenation‐sensitive functional groups, as well as the direct synthesis of imines from nitroarenes and aldehydes or ketones in the presence of such substituents. Furthermore, we introduce the first base‐metal‐mediated direct synthesis of benzimidazoles from nitroarenes and aldehydes. Functional groups that are easy to hydrogenate are again well tolerated.     

Buchwald–Hartwig Amination of Nitroarenes

The Buchwald–Hartwig amination of nitroarenes was achieved for the first time by using palladium catalysts bearing dialkyl(biaryl)phosphine ligands. These cross‐coupling reactions of nitroarenes with diarylamines, arylamines, and alkylamines afforded the corresponding substituted arylamines. A catalytic cycle involving the oxidative addition of the Ar−NO₂ bond to palladium(0) followed by nitrite/amine exchange is proposed based on a stoichiometric reaction.     

Substituent effects on the electrophilic activity of nitroarenes in reactions with carbanions

The effect on electrophilic activity of substituents located para, ortho, and meta to the nitro group of nitrobenzenes was determined by using vicarious nucleophilic substitution of hydrogen (VNS) with the carbanion of chloromethyl phenyl sulfone (1) as the model process. Values for the relative activities of substituted nitroarenes are given relative to nitrobenzene, which was taken as the standard. This process was chosen as a model reaction because it meets key criteria, such as the wide range of substituents that can be present on the nitrobenzene ring, a low sensitivity to steric hindrance, and in particular the possibility of ensuring conditions in which the overall relative rates of reaction in competitive experiments are equal to the relative rates of nucleophilic addition. The values of relative rates of addition, which were taken to be a measure of electrophilic activity, were determined by competitive experiments in which pairs of nitroarenes competed for the VNS reaction with carbanion of 1. A comprehensive set of data for effects of substituents on the electrophilic activity of nitroarenes is presented for the first time.     

Ruthenium-catalyzed tertiary amine formation from nitroarenes and alcohols

A highly selective ruthenium-catalyzed C-N bond formation was developed by using the hydrogen-borrowing strategy. Various tertiary amines were obtained efficiently from nitroarenes and primary alcohols. The reaction tolerates a wide range of functionalities. A tentative mechanism was proposed for this direct amination reaction of alcohols with nitroarenes.     

硝基芳烃与醇还原胺化:催化剂和催化机制

胺类化合物由于其化学结构和性质上的特点,在合成药物、染料和精细化学品等方面有着重要的应用。胺类化合物的合成方法很多,其中硝基芳烃与醇还原胺化反应由于可以“一锅”法将性质稳定、来源广泛的硝基芳烃、醇转化为各类胺类化合物,且无需提供额外的氢源,从而成为研究的热点。本文即以硝基芳烃与醇还原胺化反应路径为主线,从催化剂及其催化机制两方面对硝基芳烃与醇还原胺化反应的研究进展进行综述,分别对已开发的贵金属催化剂、光催化剂及一些其他类型催化剂作了介绍,重点阐述了催化剂的催化性能、底物适用范围和催化机制。尽管目前各类催化体系都已取得较大的进展,但在一定程度上依然存在着催化剂成本高,底物适应性窄,需要大量使用碱性助剂、溶剂、供氢试剂等问题。基于以上问题,本文指出硝基芳烃与醇还原胺化应重点发展绿色高效、廉价、普适性好、通用性强的催化体系;同时,还要系统地对各种催化剂的催化机制进行深入的研究,为催化体系的开发提供指导。     

Preparation of Polymers with Viologen Moieties and Their Application to the Selective Reduction of Substituted Nitroarenes

Abstract

Polymers with viologen moieties were synthesized by using poly-chlorethyl vinyl ether (PCEVE) as mother supports. These polymers were used as electron-transfer catalysts (ETC) for the reduction of substituted nitroarenes under heterophase conditions (reductant: Na₂S₂O₄ in CH₂CI₂-H₂O). The experimental results show that the substituted nitroarenes were reduced selectively and efficiently to the corresponding aniline derivatives in the presence of viologen polymers. The catalytic active species of viologen were detected by ESR and electrochemical methods. It was found that the viologen cation radical (V⁺) acts as the active species during the viologen-mediated reduction of substituted nitroarenes.     

Separation and analysis of nitroarenes from airborne particulate organic matter by HPLC and capillary GC-MS methods

Normal-phase HPLC has been applied to the separation of nitroarenes from dichloromethane extracts from airborne particulate matter samples collected in urban regions of Upper Silesia. GC-MS and capillary gas chromatography with NP detector analysis of the nitroarene fraction made it possible to identify and determine quantitatively those compounds which dominate in the organic matter emitted to the atmosphere in highly industrialized regions (2-nitrofluorene, isomeric nitroarenes of MW = 247, i.e. nitropyrene/nitrofluoranthene/nitroacephenanthrylene).     

A photocatalytic green system for chemoselective reduction of nitroarenes

A highly efficient photocatalytic reduction of nitroarenes using TiO₂/polyethylene glycol 400-water (TiO₂/PEG–H₂O) is reported. This system at deoxygenated and illuminated (sunlight or violet LED) conditions efficiently reduced nitroarenes using oxalic acid or ammonium formate as a sacrificial electron donor. Reducible functional groups such as chloro, hydroxy, flouro, bromo and carbonyl were intact under the optimized reaction conditions. The 0.1 and 0.5–1 mmol amount of nitroarenes was used under sunlight and violet LED (400 nm) irradiation, respectively. Reusability of the nanotitania was successfully carried out four times. The analyses of the recovered catalyst after five runs including TEM, XRD, TGA and CHN were done and results showed that PEG is located on TiO₂; no change in morphology, crystallinity and particle sizes was observed.     

Efficient and highly selective iron-catalyzed reduction of nitroarenes

Pyrolysis of iron-phenanthroline complexes supported on carbon leads to highly selective catalysts for the reduction of structurally diverse nitroarenes to anilines in 90-99% yields. Excellent chemoselectivity for the nitro group reduction is demonstrated.     

Investigation of the catalytic activity of metallic copper and copper dispersed SiO2 for the reductive acetylation of aromatic nitro compounds

Research on Chemical Intermediates - N-Arylacetamides such as acetaminophen are important systems in medicinal chemistry. Reductive acetylation of nitroarenes is noted to be an efficient route for...     

Mild and Efficient PtO2-Catalyzed One-Pot Reductive Mono-N-alkylation of Nitroarenes

A mild and efficient one-pot reductive monoalkylation of nitroarenes has been described using aldehydes as alkylating agents, molecular hydrogen as a reducing agent, and PtO₂ as a catalyst in methanol. This methodology is found to be applicable for both aliphatic and aromatic aldehydes and for a wide variety of nitroarenes.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Commuications® to view the free supplemental file.     

Nitroarene products from the gas-phase reactions of volatile polycyclic aromatic hydrocarbons with the OH radical and N2O5

The nitroarene products of the gas-phase reactions of acenaphthylene, acenaphthene, phenanthrene, and anthracene-d₁₀ with N₂O₅ and the OH radical (in the presence of NO_x) are reported. The calculated atmospheric lifetimes of these polycyclic aromatic hydrocarbons (PAH), as well as those of naphthalene, 1- and 2-methylnaphthalene, biphenyl, fluoranthene, pyrene, and acephenanthrylene, show that reaction with the OH radical is the dominant loss process for these PAH, with the exception of acenaphthylene, acenaphthene, and acephenanthrylene which contain an external cyclopenta-fused ring. For these latter PAH, reaction with the NO₃ radical, and for acenaphthylene and acephenanthrylene reaction with O₃, are also expected to be important atmospheric loss processes. The nitroarenes observed as products of the atmospherically-important gas-phase reactions of the PAH in environmental chamber studies are compared with the nitroarenes measured in ambient air samples collected in California. It is concluded that although nitroarenes are formed in low yields (?5%) from the OH radical-initiated reactions of the PAH, atmospheric formation of nitroarenes may contribute significantly to ambient nitroarene concentrations.     

High yield synthesis of intrinsic, doped and composites of nano-zinc oxide using novel combinatorial method

A novel synthesis of the production of luminescent zinc oxide (ZnO), either in its intrinsic, metal, non-metal-doped or composite forms with high yield has been developed by parallel iterative techniques, within a combinatorial library prepared by the reduction of nitroarenes. The reduction of nitroarenes by aluminium/zinc dusts in alkaline medium (pH 10±2) forms azoxy compounds, whereas in acidic medium (pH 4.9±0.2) forms phenyl hydroxylamine and zinc/aluminium dust gets oxidised into respective hydroxide. Here, we demonstrate the reduction of nitroarenes at neutral pH (7.0±0.2), which forms intrinsic as well as doped ZnO at 50±5°C using zinc dust alone or mixtures of salts of several transition and non-transition metals in presence of 1:10 ratio of solvent and water. Interestingly, it is observed that the photoluminescence emission could be tuned in a wide range from 390 to 615 nm useful for many display related devices.     

Green and highly efficient approach for the reductive coupling of nitroarenes to azoxyarenes using the new mesoporous Fe3O4@SiO2@Co–Zr–Sb catalyst

Research on Chemical Intermediates - Efficient, green, simple and environmentally friendly approach for the straightforward reductive coupling of nitroarenes to the corresponding azoxyarenes has...     

Reactions of nitroheteroarenes with carbanions: bridging aromatic, heteroaromatic, and vinylic electrophilicity

The relative rate constants for the vicarious nucleophilic substitution (VNS) of the anion of chloromethyl phenyl sulfone (1-) with a variety of nitroheteroarenes, for example, nitropyridines, nitropyrroles, nitroimidazoles, 2-nitrothiophene, and 4-nitropyrazole, have been determined by competition experiments. It was shown that nitropyridines are approximately four orders of magnitude more reactive than nitrobenzene. Among the five-membered heterocycles 2-nitrothiophene is the most active followed by nitroimidazoles and 4-nitropyrazole. Nitropyrroles are the least electrophilic nitroheteroarenes with reactivities comparable to nitrobenzene. Quantum chemically calculated methyl anion affinities (B3LYP/6-311G(d,p)//B3LYP/6-31G(d)) of the nitroarenes correlated only moderately with the partial relative rate constants. The correlation of these activities with the LUMO energies of nitroarenes is even worse. By measuring the second-order rate constants of the addition of 1- to nitroarenes and to diethyl arylidenemalonates 10, it was possible to link the electrophilic reactivities of nitroheteroarenes with the comprehensive electrophilicity scale based on the linear-free-energy-relationship log k(20 degrees C)=s(N+E).     

Gold nanoparticles anchored onto the magnetic poly(ionic‐liquid) polymer as robust and recoverable catalyst for reduction of Nitroarenes

Gold nanoparticles supported on poly ionic‐liquid magnetic nanoparticles (MNP@PIL@Au) were synthesized by reduction of HAuCl4 with sodium borohydride. The synthesized catalyst was characterized using by AAS, TEM, FT‐IR, EDS, TGA and XRD techniques. The performance of the synthesized catalyst was investigated in the reduction of nitroarenes with NaBH₄. The reaction was carried out for various nitroarenes in water and mild conditions with high yields. The catalyst selectivity for the reduction of nitro group in the presences of other functional groups such as halides and alkynes was fairly well. The recycling of the catalyst was done 8 times without any significant loss of its catalytic activity.