Preparative-scale synthesis of amino coumarins through new sequential nitration and reduction protocol

In contrast to the conventional deleterious approach for nitration (for example HNO₃/H₂SO₄) and for reduction (for example Zn/HCl), we hypothesized that sensitive heterocycles such as coumarins could not withstand with those hard conditions. Hence, while studying this reaction sequence to prepare amino coumarins (which is our ongoing project to synthesize antitubercular coumarin agents), we came across mild and greener reagent for nitration using calcium nitrate (Ca(NO₃)₂·4H₂O; lime nitrate), and reduction using d-glucose. These two mild, chemoselective, high yielding methods are discussed herein.     

A convenient synthetic route to a useful synthon: 4-bromo-2-pyridinecarboxaldehyde

We have developed a novel four-step method to synthesise 4-bromo-2-pyridinecarboxaldehyde, from 2-picoline-N-oxide via 4-nitro-2-pyridinecarboxaldehyde, under mild reaction conditions.     

经典有机合成反应中的新方法

综述了载体、分子筛等在经典有机合成中的应用.与传统的合成方法相比,它们具有反应条件温和、操作方便、提高收率或缩短反应时间等优点,甚至可以使某些在传统条件下不能进行的反应发生.参考文献40篇.     

Selective nitration of phenols using bismuth subnitrate/charcoal in the presence of trichloroisocyanuric acid under aprotic conditions

<正>A mild,efficient and regioselective method for the mononitration of phenolic compounds is described using bismuth subnitrate/ charcoal in the presence of trichloroisocyanuric acid in CH_2Cl_2 at room temperature.     

High intensity ultrasound-assisted reduction of sterically demanding nitroaromatics

Sterically demanding nitroaromatic compounds have been prepared and reduced to their corresponding amines with high intensity ultrasound using hydrazine in the presence of a Raney nickel catalyst. These reactions were dependent on catalyst quality, solvent and ultrasonic amplitude and, in comparison to their silent reactions, proceeded much faster and afforded higher yields.     

Further insight into aryl nitration of tetraphenylporphyrin

We report an in-depth study on meso-aryl nitration of tetraphenylporphyrin. In contrast to previous studies, new evidence reveals that tetrakis(p-nitrophenyl) derivative can be obtained as a major product. Successful isolation of the barely soluble product toward a remarkable yield of nearly 90% has been reached by means of a solid phase extraction technique. Distribution of different nitro-porphyrin components is reassessed with respect to varying acid content in the reactions. An ortho-effect model is proposed to describe the formation mechanism.     

Trichloroisocyanuric acid (TCCA) and carboxamide interactions in TCCA/NaNO2 triggered nitration of pyrrole and indole in aqueous aprotic media: A kinetic correlation of solvent properties with reactivity

This study deals with the trichloroisocyanuric acid (TCCA) interactions with carboxamides like formamide (FMA), N,N′‐dimethyl formamide (DMF), and N,N′‐dimethyl acetamide (DMA) interactions during the nitration of heterocyclic compounds (HC) like pyrrole and indole in the presence of excess of [NaNO₂] over the concentrations of all other reactants. All the reactions were performed in aqueous acetonitrile media containing carboxamide under acid‐free conditions. Kinetics of the reactions revealed first order in [nitrating agent] and [HC] under otherwise similar conditions. To gain an insight into the reactive species and role of added carboxamide (FAA, DMF, DMA, etc.), the observed rates of the nitration reaction (log k) were analyzed as a function of (1/D), ([D ? 1]/[2D + 1]), mole fraction (n_x), and volume (%) of carboxamide, 1/viscosity, density refractive index function), and Hildebrand solubility parameter plots. Linear regression analysis gave very good correlation coefficients (R² values), which indicate the importance of several solvent properties in addition to the role of dielectric constant (D) of the reaction media. Multiple linear solvent energy relationships suggested by Abraham, Koppel, Palm, and Taft also afforded very good correlation coefficient (R² values), showing the importance of cumulative effect of solvent properties. Besides these features, the negative entropies of activation (?S^#) suggest greater solvation in the transition state. Isokinetic temperature (β) values for different protocols were very close to the experimental temperature range (303‐323 K), indicating the importance of both enthalpy and entropy factors in controlling the reaction.     

Energetic materials based on poly furazan and furoxan structures

Furazan and furoxan represent fascinating explosophoric units with intriguing structures and unique properties. Compared with other nitrogen-rich heterocycles, most poly furazan and furoxan-based heterocycles demonstrate superior energetic performances due to the higher enthalpy of formation and density levels. A large variety of advanced energetic materials have been achieved based on the combination of furazan and furoxan moieties with different kinds of linkers and this review provides an overview of the development of energetic poly furazan and furoxan structures during the past decades, with their physical properties and detonation characteristics summarized and compared with traditional energetic materials. Various synthetic strategies towards these compact energetic structures are highlighted by covering the most important cyclization methods for construction of the hetercyclic scaffolds and the following modifications such as nitrations and oxidations. Given the synthetic availabilities and outstanding properties, energetic materials based on poly furazan and furoxan structures are undoubtedly listed as a promising candidate for the development of new-generation explosives, propellants and pyrotechnics.     

Peroxynitrite Scavenging Activities of Resveratrol and Piceid

In vitro antioxidant activities of resveratrol and piceid against peroxynitrite(ONOO^-) were examined by the inhibition of 3-nitrotyrosine formation. Trolox was used as a positive control. Resveratrol and piceid exhibited high ONOO^--scavenging activities in a concentration dependent manner. The antioxidant activities(the concentration of test compound required to yield a 50% inhibition of tyrosine nitration, IC₅₀) of resveratrol and piceid against ONOO^- were (48.34±0.97) and (74.69±1.49) μmol/L, respectively. Compared with that of trolox[(105.40±1.16) μmol/L], their scavenging activities were 2.2- and 1.5-fold higher for resveratrol and piceid. Formation of nitro-resveratrol as shown by UV-Vis spectroscopy and liquid chromatography-tandom mass spectrometry(LC-MS/MS) analysis indicates that resveratrol could directly scavenge ONOO^- via nitration reaction. Our results demonstrate that foods and medicinal herbs with resveratrol and piceid as stronger ONOO^- scavengers are valuable ingredients and have healthy application in preventing humans from peroxynitrite-mediated oxidative damage by scavenging peroxynitrite efficiently.     

连续流微反应器中微纤结构化的Nafion/SiO2固体酸催化苯硝化反应

采用溶胶-凝胶组装方法制备了Nafion/SiO2胶体, 并涂附于烧结的316L不锈钢(SS-316L)金属微纤网络, 形成了空隙率为60%-75%(φ, 体积分数)的整体式微纤结构化的Nafion/SiO2固体酸催化剂. 使用傅里叶变换红外光谱(FT-IR), 热重分析(TGA), 扫描电子显微镜(SEM)及NH3吸附法对微纤结构化的Nafion/SiO2催化剂进行了表征. 结果显示, 溶胶-凝胶组装方法可以明显促进Nafion的分散, 导致酸性中心的暴露量显著增加; 结构化的Nafion/SiO2催化剂以200-400 nm颗粒堆积而成的多孔涂层形式存在. 在一种集换热、混合、催化(反应)功能于一体的微反应器中, 考察了整体式微纤结构化的Nafion/SiO2固体酸催化剂催化苯硝化的反应性能. Nafion在SiO2中的组装量为20%(w, 质量分数), 金属微纤网络上Nafion/SiO2担载量为36.3%(w)的优化催化剂上, 75 ℃时苯转化率为44.7%, 硝基苯选择性可达99.9%. 相近转化率下, Nafion/SiO2固体酸单位酸中心的催化效能约为硫酸的600倍.