2,5-二甲氧基-4-氯硝基苯与硫化钠的反应

硫化钠和二硫化钠分别在95%乙醇中与2,5-二甲氧基-4-氯硝基苯反应, 原本期望得到2,5-二甲氧基-4-氯苯胺, 然而对产物结构的1H NMR, 13C NMR, MS以及元素分析结果表明, 2,5-二甲氧基-4-氯硝基苯中的硝基没有被硫化钠和二硫化钠还原成氨基, 而是其中的氯原子被硫离子(或二硫离子)取代, 分别生成了4,4’-硫代-2,2’,5,5’-四甲氧基-双硝基苯和4,4’-双硫代-2,2’,5,5’-四甲氧基-双硝基苯. 根据这个实验事实, 讨论了上述亲核取代反应的机理.     

A Facile Synthetic Route to L-Phosphinothricin

Phosphinothricin, the active ingredient of the well known broad-spectrum herbicideglufosinate-ammonium, is a naturally occurring amino acid possessing the uniquemethylphosphinate moiety, and its strong herbicidal activity has been attributed to anability to inhibit glutamine synthetase in plants and bacteria1. Further research showedthat L-enantiomer of phosphinothricin was the carrier of the activity, whereas the D formonly had a small action2, therefore the stereoselective synthesis of L-pho…     

A Novel Method of Preparing Unsymmetrical Thioether from Disulfides

The disulfides reacted with zinc in DMF, followed by alkyl halides, giving unsymmetrical thioether in excellent yields. This reaction takes place under mild and neutral conditions.     

A Facile Synthesis Route to 1,3-dichlorodisilazanes

Since the pioneering work of Verbeek', considerable attention has focussed on researchdevoted to the preparation of silicon nitride- and silicon carbide- based ceramic materials.Owing to their promising potential for the formation of high-purity non-oxide siliconbased ceramics, organosilicon compounds (precursors) have attracted considerableinterest in recent years 2. The structures and the chemical composition of the precursorsstrongly effect the properties of the final ceramic materials. Acc…     

Poly(arylene sulfide)s via nucleophilic aromatic substitution reactions of halogenated pyromellitic diimides

Nucleophilic aromatic substitution (SNAr) reactions are exploited to prepare poly(arylene sulfide)s (PAS's) via the reaction of bis-thiolates and dibrominated pyromellitic diimide (PMDI) derivatives. Small-molecule model studies reveal the reaction is well-defined and proceeds in quantitative yield in practical times at room temperature. Variation in comonomer feed ratios allowed some control over target polymer molecular weights in the step polymerization, but control was likely limited by the relatively poor polymer solubility in the dipolar aprotic solvents typically employed to promote SNAr reactions. One substitution pattern produces a steric “pocket” around the PMDI units, inducing a peculiar solubility trend in halogenated solvents; that is, greatly reduced solubility in CHCl₃ relative to CH₂Cl₂ and C₂H₂Cl₄. One example small-molecule readily dissolves in CHCl₃ at room temperature, then rapidly grows poorly soluble crystals revealed by single-crystal XRD to contain CHCl₃ molecules in the steric pockets. Finally, the recently demonstrated depolymerization of phthalonitrile-based PAS's via ipso substitution with monothiolates as chain scission agents yields quantitative molecular weight reduction to monomeric species from the polymers reported here.     

Construction of 5H-Dibenzo[c,e]azepine Framework from Dibenzothiophene Dioxides and N-Benzylimines through SNAr Reactions

Treatment of a mixture of dibenzothiophene dioxides and benzaldehyde N-benzylimines with potassium hexamethyldisilazide induces sequential intermolecular and intramolecular S_NAr reactions to eventually form the corresponding 5H-dibenzo[c,e]azepines without any formation of the conceivable five-membered fluorene derivatives.     

简捷溶剂热技术制备纳米棒基PbS树枝晶

以氯化铅和硫氰酸钾为原料,乙二醇为溶剂,采用简捷溶剂热技术制备了半导体PbS纳米棒基树枝晶。粉体用XRD、XPS、FESEM、TEM和ED进行了表征。单个PbS树枝晶具有三维空间结构,由一个主干和四个相互垂直侧枝组成。主干长2～10 μm,直径150～300 μm,每组侧枝纳米棒相互平行,沿主干垂直生长,棒长0.1～1.5 μm,直径80～180 nm。并对生长过程进行了探讨。     

基于新型不对称BODIPY的GSH荧光探针

本文通过在BODIPY母体中引入丙二腈,设计合成了一个新型不对称BODIPY荧光染料CN-B-Cl。由于丙二腈强吸电作用,荧光染料CN-B-Cl具有优异的化学活性,能够与含巯基的化合物在buffer体系中迅速发生芳香亲核取代反应;与GSH反应生成硫取代BODIPY,而与Cys/Hcy反应生成氮取代BODIPY。根据不同取代基BODIPY化合物发光性能的不同,该荧光探针可选择性区分GSH与Cys/Hcy。     

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。     

Simulation of texture evolution for nematic liquid crystalline polymers under shear flow

The development of microstructure in nematic liquid crystalline polymers under shear flow is investigated through computational simulation. By using a tensorial expression for the elastic torque, the nemato-dynamic equation is numerically resolved. The simulation shows that elastic anisotropy has a strong influence on the evolution of the director and that the ‘log-rolling’ orientation of the directors emerges for tumbling nematics if the twist constant is smaller than the splay and the bend constants, even though one starts from a structure in which the directors are aligned within the velocity and velocity gradient plane. The interaction of wedge disclination pairs subject to a shear flow field is also simulated. The generation, multiplication and interaction of inversion wall defects during shearing have been revealed. In general the wall moves to the boundaries and is absorbed by the boundaries. When two walls of opposite orientation meet, a loop may form, then shrink, and finally collapse. Correspondingly, if they have the same orientation, commutation will occur.     

在离子液中无水碳酸钾参与的串联甲磺酸取代苯酯脱保护和芳香亲核取代反应来合成不对称二芳醚

本文报道了一种在离子液[Bmim]BF4中，由无水碳酸钾参与的串联甲磺酸取代苯酯脱保护和芳香亲核取代反应来合成不对称二芳醚的方法。离子液可以循环使用多次，而且此实验操作具有便捷、实用与环境友好的特点。     

Reinvestigation of the noncatalyzed coupling of aryllithium with haloarene: a novel aromatic nucleophilic substitution pathway

Noncatalyzed coupling reactions of aryllithiums and haloarenes proceed not only through the well-known aryne route but also, in some cases, through a novel addition-elimination pathway. Indeed, ortho-chloro- and ortho-bromomethoxyarenes lead selectively to the corresponding ortho-biaryls through a chelation-driven aromatic nucleophilic substitution pathway. Contrary to common belief, such noncatalyzed coupling reactions often proceed with high regioselectivity and high yield. These results underline the potency of such simple reactions and open up a straightforward access to a wide range of biaryl structures; this also appears particularly useful for large-scale and biaryl building-block syntheses, as only cheap and readily available substrates are involved.     

A Facile Route to Indolo

Treatment of 1-(2'-bromobenzyl)-3,4-dihydroisoquinolines 2 in the presence of K(2)CO(3) in boiling DMF efficiently provided a variety of alkoxy-substituted indolo[2,1-a]isoquinolines 3. Application of this cyclization to 7-benzyloxyisoquinoline derivatives, followed by further elaboration of the resultant 2-benzyloxy-5,6-dihydroindolo[2,1-a]isoquinolines 16a,b, led to the formal synthesis of dibenzopyrrocoline alkaloids, (+/-)-cryptaustoline (1a) and (+/-)-cryptowoline (1b).     

Competition between Nucleophilic Substitution of Halogen (SNAr) versus Substitution of Hydrogen (SNArH)—A Mass Spectrometry and Computational Study

The mechanism of intramolecular gas‐phase reactions of N‐(2‐X‐5‐nitrophenyl)‐N‐methylacetamide carbanions (X=H, F, Cl) has been studied using negative ion electrospray mass spectrometry ((?)ESI‐MS) technique and modelled computationally. It was proven that all three anions form cyclic σ^H adducts, which undergo elimination of water. In the case of X=F, formation of the σ^F adduct, leading to S_NAr reaction, was a competing process. This is the first proof that also in the gas phase formation of σ^H adduct proceeds faster than σ^X adduct and only when X=F, rates of these two processes are comparable. The experimental results are in full agreement with quantum chemical calculations.     

Synthesis and Reactions of Trifluoromethyl-Substituted 1,3,5-Triazines

A variety of di- and trifluoromethyl-s-triazines are prepared following straightforward synthetic protocols from simple, commercially available starting materials. Trichloromethyl-substituted triazine electrophiles are obtained in good yield and react with amine nucleophiles to afford aminotriazine products in good to excellent yield. The nucleophilic aromatic substitution reaction is broad in scope and proceeds smoothly with both aromatic and aliphatic (primary, secondary, and branched) amines in the presence of non-participating functional groups including alcohols, carboxylic acids, indoles, and common amine protecting groups. Furthermore, most reactions require only a catalytic amount of 4-DMAP with no stoichiometric base and are complete within two hours at ambient temperature.     

Efficient synthesis of unsymmetrical diaryl thioethers via TBAF-mediated denitrative substitution of nitroarenes with PhSTMS under mild and neutral conditions

Tetrabutylammonium fluoride(TBAF) effectively facilitated a denitrative substitution reaction of electron-deficient nitroarenes with phenylthiotrimethylsilane(PhSTMS) under mild and base-free neutral conditions at room temperature,providing a practical and efficient synthesis of useful unsymmetrical diaryl thioethers.Nitroarenes bearing ortho-and para-positioned electron-withdrawing groups are the most reactive substrates,indicating that this reaction most possibly proceeded via the nucleophilic aromatic substitution(S_NAr) mechanism.