2,4-二硝基酚与二氟溴甲基膦酸二乙酯反应的研究

酚在碱性条件下与卤代烃反应生成相应的芳香醚,是典型的亲核取代反应,对于2,4-二硝基酚和二氟溴甲基膦酸二乙酯在碱性条件下的反应,其实验过程包括室温中和,甲苯回流脱水和亲核取代等三步反应。对产物进行了提纯和一系列的表征,结果发现主要生成了一种酚醚化合物。     

一种新的芳香族亲核取代反应机理——S_(RN) 1

一、引言化学家早已熟悉芳香族亲核取代反应主要按这种机理进行取代的芳香化合物,要求在被取代基团的邻位或对位有很强的拉电子基团,特别要求有硝基存在,以产生活化作用。     

芳香族化合物亲核取代及应的机理

芳香族化合物核上取代反应包括一种键的生成和一种键的破坏。若这种新生的键的一对电子由芳香核给予,也就是取代试剂以零个电子参与键的构成,称为亲电取代反应;若芳香核和取代试剂各以一个电子构成新键,则称为游离基取代反应;若这种新键的一对电子是由取代试剂单方面提供,则称为亲核取代反应。可以举出下面两种反应作为芳香族化合物亲核取代反应的例子:     

芳基离子及芳基自由基与 环己二烯离子及环己二烯自由基的区别

通过比较芳香亲电取代与芳基重氮盐的水解反应和芳香亲核取代与芳基金属有机试剂参与的反应中芳香部分结构的差别来说明芳基正离子与环己二烯正离子以及芳基负离子与环己二烯负离子的区别。讨论了芳香自由基偶联中的芳基自由基及其对芳香环的自由基加成中的环己二烯自由基的差别。还讨论了芳基离子和自由基结构与芳香性的关系。反应中涉及芳烃芳香环碳原子的sp2杂化轨道形成的σ键断裂时,苯环的6电子大π键不被破坏,根据电子转移的情况,可以形成芳基正离子、芳基负离子或芳基自由基。而亲电试剂、亲核试剂或自由基对芳烃的苯环π键发生的加成反应,都会破坏苯环的6电子大π键,使其失去芳香性,相应地形成环己二烯正离子、环己二烯负离子和环己二烯自由基中间体。     

4-肟醚基喹唑啉类化合物的合成及其抗植物病毒TMV活性

4-氯喹唑啉与取代芳香肟在碱存在下进行亲核取代反应,合成了17种新型肟醚基喹唑啉衍生物,并对其结构进行了表征。生物活性测试表明,部分化合物抗植物烟草花叶病毒活性超过抗植物病毒商品药剂2,4-二氧六氢-1,3,5-三嗪。     

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。     

4—肟醚基喹唑啉类化合物的合成及其抗植物病毒TMV活性

４－氯喹唑啉与取代芳香肟在碱存在下进行亲核取代反应，合成了１７种新型肟醚基喹唑啉衍生物，并对其结构进行了表征。生物活性测试表明，部分化合物抗植物烟草花叶病毒活性超过抗植物病毒商品药剂２，４－二氧六氢－１，３，５－三嗪。     

芳香酮结构与烯烃加成反应中的区位选择效应的理论研究

研究了芳香酮与烯烃在RuH2(CO)(PPh3)3催化剂催化下发生亲核加成反应生成邻位产物的区位选择效应规律. 采用从头算方法优化得到了12种芳香酮反应物的稳定结构, 研究了共轭效应、电子效应和立体效应对反应活性和选择性的影响, 提出了芳香酮上b位碳原子与羰基在LUMO轨道中形成平面"U弯区"是进行加成反应的必要条件. 在同类骨架结构芳香环上, 相同位置的取代原子不同, b位碳原子的正电荷越大, 生成邻位产物速度越快, 产率相应较高. 当羰基上氧原子与芳香环上邻位碳原子距离达到一定数值, 立体效应占主导位置, 最佳反应距离为0.27~0.30 nm. 同时, 提出芳香酮催化加成反应的可能机理是经过了Ru催化剂与芳香酮上共轭结构的形成, 1, 2氢迁移造成C-H键的断裂而进行的.     

芳香取代的几种新方法

本文介绍了芳香取代的几种新方法及其在有机合成中的应用。主要包括：（１）Ｖｉｃａｒｉｏｕｓ亲核取代，（２）邻位金属化定向反应，（３）钯催化的取代方法等。     

铁粉促进断裂Se—Se键及其应用于合成α-芳硒基羰基化合物

在铁粉存在下,以商用N,N-二甲基甲酰胺(DMF)作溶剂,90℃、氮气保护下,二芳基二硒醚与α-溴代羰基化合物反应,得到一系列α-芳硒基羰基化合物.考察了温度、时间、溶剂及铁粉用量对反应的影响,其中,温度对反应的影响最为明显.α-溴代羰基化合物中羰基上取代基对反应有很大影响,取代基为苯基时,转化率较甲基或烷氧基时低.反应机理可能是铁插入Se—Se键中形成亲核性Se Fe Se,随后与亲电底物α-溴代羰基化合物发生亲核取代.本方法使用铁粉促进断裂Se—Se键具有原料安全无毒、廉价易得、实验操作简便等优点.     

Synthesis and thermal transformations of allyl aryl ethers of adamantane series

Allyl aryl ethers of adamantane series were obtained by reacting (E)-1-(adamant-1-yl)-3-bromoprop-1-ene with phenol or ethyl salicylate. The features of thermal transformations of allyl aryl ethers containing bulky adamantane scaffold were investigated. It has been found that the composition of the reaction products is largely dependent on temperature, time and nature of the solvent. When a nucleophilic solvent was used, the reaction proceeded via formal substitution of phenoxy fragment with nucleophilic species prevailing in the reaction medium.     

Catalytic SNAr Hexafluoroisopropoxylation of Aryl Chlorides and Bromides

Fluoroalkyl aryl ethers are valuable structural motifs in pharmaceuticals because compounds with these motifs are more metabolically stable and more lipophilic than their nonfluorinated analogues. However, hexafluoroisopropyl aryl ethers have not been extensively studied, presumably because of the lack of efficient synthetic methods. Herein, we describe a rhodium-catalyzed nucleophilic aromatic substitution of aryl chlorides or bromides, which act as the limiting reagents, with weakly nucleophilic hexafluoro-2-propanol under mild reaction conditions. This method provides diverse hexafluoroisopropyl aryl ethers. We demonstrated the generality of this method by carrying out reactions of a large array of unactivated aryl halides, and we found that the success of the reactions relied on arene activation by means of η⁶-coordination.     

P(i-BuNCH2CH2)3N: an efficient promoter for the nucleophilic aromatic substitution reaction of aryl fluorides with aryl TBDMS (or TMS) ethers

[reaction: see text]. The nucleophilic aromatic substitution reaction between electron-deficient aryl fluorides and aryl TBDMS (or TMS) ethers has been shown to be efficiently promoted by proazaphosphatranes such as P(i-BuNCH(2)CH(2))(3)N (3). Excellent yields of diaryl ether products were obtained under unusually mild conditions.     

Benzyl protection of phenols under neutral conditions: palladium-catalyzed benzylations of phenols.

Benzyl protection of phenols under neutral conditions was achieved by using a Pd(eta3-C3H5)Cp-DPEphos catalyst. The palladium catalyst efficiently converted aryl benzyl carbonates into benzyl-protected phenols through the decarboxylative etherification. Alternatively, the nucleophilic substitution of benzyl methyl carbonates with phenols proceeded in the presence of the catalyst, yielding aryl benzyl ethers.     

C(aryl)-O bond formation from aryl methanesulfonates via consecutive deprotection and S(N)Ar reactions with aryl halides in an ionic liquid

An efficient K3PO4-mediated synthesis of unsymmetrical diaryl ethers using the ionic liquid [Bmim]BF4 (1-butyl-3-methylimidazolium tetrafluoroborate) as solvent has been developed. The procedure involves consecutive deprotection of aryl methane-sulfonates and a nucleophilic aromatic substitution (S(N)Ar) with activated aryl halides.     

A practical synthesis of aryl tetrafluoroethyl ethers via the improved reaction of phenols with 1,2-dibromotetrafluoroethane

An efficient and practical synthesis of various aryl tetrafluoroethyl ethers by the reaction of phenols with 1,2-dibromotetrafluoroethane and the subsequent reduction with zinc dust was described. The nucleophilic substitution of 1,2-dibromotetrafluoroethane with phenols initiated by bromophilic attack was improved by using Cs₂CO₃ as a base and DMSO as a solvent.     

Intramolecular Aryl Migration of Diaryliodonium Salts: Access to ortho‐Iodo Diaryl Ethers

By using vicinal trifluoromethanesulfonate‐substituted diaryliodonium salts, a novel approach was developed for the synthesis of ortho‐iodo diaryl ethers by intramolecular aryl migration. The reaction conditions are mild with a broad substrate scope. Mechanistic insight suggests a sulfonyl‐directed nucleophilic aromatic substitution pathway. Additionally, the product ortho‐iodo diaryl ethers serve as versatile synthons as demonstrated with several coupling reactions. Furthermore, a useful thyroxine analogue of the 3‐iodo‐l ‐thyronine (3‐T₁) derivative was synthesized by this aryl migration procedure.     

Diphenyl disulfide and sodium in NMP as an efficient protocol for in situ generation of thiophenolate anion: selective deprotection of aryl alkyl ethers and alkyl/aryl esters under nonhydrolytic conditions

Aryl methyl ethers, methyl esters, aryl esters, and aryl sulfonates are chemoselectively deprotected under nonhydrolytic conditions by treatment with Ph(2)S(2) (0.6 equiv) and Na (1.6 equiv) in NMP under reflux or at 90 degrees C. Quantitative utilization of the 'PhS' moiety as the effective nucleophilic species represents conservation of atom economy. Other solvents such as HMPA, DMPU, DMEU, and DMF afforded comparable results. Chloro, nitro, aldehyde, alpha,alpha-diketone, and alpha,beta-unsaturated ketone functionalities remain unaffected. The deprotection was found to take place in the order aryl ester > alkyl ester > aryl alkyl ether. Substrates bearing strong electron-withdrawing groups react at a faster rate than those not having such substitution. The differences in rate of reaction has been exploited for selective deprotection for intramolecular competition. An aryl acetate/benzoate is deprotected selectively in preference to a methyl ester or aryl methyl ether. Selective deprotection of a methyl ester is observed in the presence of an aryl alkyl ether.     

An application of arene–iron chemistry in the synthesis of a novel liquid crystalline polymer

Arene–iron chemistry was applied in the synthesis of a novel liquid crystalline polymer. The chemistry, which is based on iron cyclopentadienyl (FeCp) arene complexes, allows sequential nucleophilic substitution of the chlorides from 1,3-dichlorobenzene–FeCp complex and photolytic decomplexation of the products to afford asymmetrical aryl ethers. This methodology provides easy access to novel polyether-esters, and is potentially useful in the synthesis of various functional polyarylates. © 1997 John Wiley & Sons, Inc.     

Single-crystal Cultivation and Structure Analysis of Unstable 1-Azido-2-chloro-4-nitrobenzene

The 1-azido-2-chloro-4-nitrobenzene was prepared by nucleophilic substitution between 2-chloro-4-nitro-1-(trifluoromethylsulfinyl)benzene and sodium azide, and its structure was characterized by NMR spectrum and X-ray single-crystal diffraction. It crystallizes in the monoclinic system, space group P21/n, Z = 8 and Mr = 198.57. A cultivation process of the single crystal of unstable aryl azide was provided. The group of trifluoromethyl sulfinyl was found for the first time to be a new excellent leaving group of aromatic nucleophilic substitution reactions.