Reactions of Osmabenzene with Silver/Copper Acetylides: From Metallabenzene to Benzene

The transformations of metallabenzene to substituted benzenes have been achieved by reactions of osmabenzenes with silver/copper acetylides. In this investigation, novel tetraphenylphosphonium salts containing two phosphonium substituents on the same benzene ring are generated.     

Enantioselective Electrophilic Aromatic Nitration: A Chiral Auxiliary Approach

Enantioselective electrophilic aromatic nitration methodology is needed to advance chirality‐assisted synthesis (CAS). Reported here is an enantioselective aromatic nitration strategy operating with chiral diester auxiliaries, and it provides an enantioselective synthesis of a C_3v‐symmetric tribenzotriquinacene (TBTQ). These axially‐chiral structures are much sought‐after building blocks for CAS, but they were not accessible prior to this work in enantioenriched form without resolution of enantiomers. This nitration strategy controls the stereochemistry of threefold nitration reactions from above the aromatic rings with chiral diester arms. Dicarbonyl‐to‐arenium chelation rigidifies the reaction systems, so that remote stereocenters position the ester‐directing groups selectively over specific atoms of the TBTQ framework. Closely guided by computational design, a more selective through‐space directing arm was first predicted with density functional theory (DFT), and then confirmed in the laboratory, to outperform the initial structural design. This enantio‐ and regioselective TBTQ synthesis opens a new pathway to access building blocks for CAS.     

Reactions of Vinylnitrosonium Ions with some Aromatic Heterocycles - Electrophilic Substitution vs Cycloaddition

Reaction of N-cyclohexyl-N-propenyl-nitrosonium ion and N-cyclohexyl-N-ethenylnitrosonium ion with indole and N-methylindole resulted in electrophilic substitution while reaction of the former with skatole, benzothiophene and benzofuran resulted in cycloaddition.     

Concerted Nucleophilic Aromatic Substitution Reactions

Recent developments in experimental and computational chemistry have identified a rapidly growing class of nucleophilic aromatic substitutions that proceed by concerted (cS_NAr) rather than classical, two‐step, S_NAr mechanisms. Whereas traditional S_NAr reactions require substantial activation of the aromatic ring by electron‐withdrawing substituents, such activating groups are not mandatory in the concerted pathways.     

大学有机化学“五维度”教学新策略——以“芳烃的亲电取代和亲核取代反应”为例

介绍了大学有机化学“强理念、重思维、活课堂、共育人、乐钻研”五维度教学新策略的内涵与实践。以线下教学为主,腾讯会议和慕课为辅助,践行“有机化学是科学也是艺术”的教学理念;采用多循环“疑探式”教学方式,辨析亲电试剂和亲核试剂的多样性;注重培养学生多种科学思维的综合运用;强化“文献预习”“练习讲解”“综合作业”“师生互动”等多个教学环节,加深学生对知识的理解与应用,提升学生在课堂中的参与度,着重培养学生的科学思维和人文素养、自主学习与团队合作精神。     

Abstraction Versus Electrophilic Substitution: Metaphosphate-Mediated Reactions in the Gas Phase

Abstract

Whereas arylmetaphosphates (ArOPO₂) tend to cyclise by intramolecular C-H insertion (phosphorylation) when generated in the gas phase, their alkyl-substituted counterparts exhibit non-electrophilic behaviour and give rise to alkenes by an unusual 1,2-methyl shift induced by a combination of hydrogen abstraction with concomitant elimination of metaphosphoric acid (HOPO₂).     

Relative Electrophilic Fluorinating Power as Assayed by Competitive Catalytic Halogenation Reactions

Catalytic fluorination/chlorination competition experiments of β‐keto ester 5 were used to assess the relative fluorinating activity of various electrophilic N? F reagents (containing an N? F bond). Thus, in the halogenation reactions catalyzed by the [Ti(TADDOLato)] complex 1 (=bis(acetonitrile)dichloro[(4R,5R)‐2,2‐dimethyl‐α,α,α′,α′‐tetra(naphthalen‐1‐yl)‐1,3‐dioxolane‐4,5‐dimethanolato(2?)‐κO,κO′]titanium), the activity range of a series of commercially available reagents spans more than two orders of magnitude. Selectfluor^TM (=1‐(chloromethyl)‐4‐fluoro‐1,4‐diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate); 9 ; also called F‐TEDA; TEDA=triethylenediamine) reacts more than 100 times faster than 1‐fluoropyridinium tetrafluoroborate.     

Electrophilic Substitution in Aromatic and Heteroaromatic Substrates by Trichlorocyclopropenylium Tetrachloroaluminate

Trichlorocyclopropenylium tetrachloroaluminate is an electrophilic reagent for the preparative introduction of a cyclopropenyl fragment into heteroaromatic and aromatic substrates.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 706–709.Original Russian Text Copyright © 2005 by Skornyakov, Lozinskaya, Proskurnina, Zefirov.     

Intramolecular Electrophilic Aromatic Substitution in Gas-phase Fragmentation of Protonated N-Benzylbenzaldimines

In this study, the gas-phase fragmentations of protonated N-benzylbenzaldimines were investigated by electrospray ionization tandem mass spectrometry (ESI-MSⁿ). Upon collisional activation, several characteristic fragment ions are produced and their fragmentation mechanisms are rationalized by electrophilic aromatic substitution accompanied by benzyl cation transfer. (1) For N-(p-methoxybenzylidene)-1-phenylmethanimine, concomitant with a loss of HCN, a product ion at m/z 121 was observed. It is proposed to be generated from electrophilic substitution at the ipso-position by transferring benzyl cation rather than cleavage of the C-N double bond. (2) For N-(m-methoxybenzylidene)-1-phenylmethanimine, a product ion at m/z 209 was obtained, corresponding to the elimination of NH₃ carrying two hydrogens from the two aromatic rings respectively. This process can be rationalized by two sequential electrophilic substitutions and cyclodeamination reaction based on the benzyl cation transfer. Deuterium-labeled experiments, density functional theory (DFT) calculation and substituent effect results also corroborate the proposed mechanism. Figure a

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知识价值视角下基于发现学习的教学探索*——以芳香亲电卤代反应为例

为了充分发挥知识的多维教育价值,促进学生发展,基于发现学习理念,以芳香亲电卤代反应为例,将基础知识与前沿文献的引入协同进行,采用问题-发现模式推动学生主动思考,引导学生探究知识的深度、广度、联系度、实践度。实践表明,通过发现学习学生能主动进行知识建构,而对知识完整深刻的处理可促使学生在学习知识的同时实现思维训练、能力培养与价值引领。     

Electrophilic Nitration of Electron-Rich Acetophenones

It is demonstrated that electron-rich disubstituted acetophenones react according to various electrophilic nitration conditions that generally lead to ipso substitution accompanying the conventional reaction. The hydroxy substituent does not seem prone to favor such behaviour.     

Electrophilic Nitration of Electron-Rich Acetophenones

Summary. It is demonstrated that electron-rich disubstituted acetophenones react according to various electrophilic nitration conditions that generally lead to ipso substitution accompanying the conventional reaction. The hydroxy substituent does not seem prone to favor such behaviour.     

Phase-transfer Catalysis in Electrophilic Substitution Reactions: IX. Kinetics and Mechanism of Nitration of Polycyclic Arenes under Conditions of Phase-transfer Catalysis in a System Benzene-Aqueous Sulfuric Acid-Sodium Nitrite

Nitration of polycyclic arenes under conditions of the phase-transfer catalysis in a system benzene-aqueous sulfuric acid-sodium nitrite involves reagent activation stage with formation of its active forms H₂NO₂ ⁺ and H₂O·NO⁺ in the polar phase. The limiting reaction stage is presumably interphase transport of the active reagent form.     

An Organization Device for Visualizing Mechanisms and Regiochemistry Rationales in Electrophilic Aromatic Substitution

Design and testing of a hand-held device, consisting of two sheets of card stock, presenting electrophilic aromatic substitution (EAS) data in an organized fashion, and designed to facilitate learning electrophilic aromatic substitution reactions is reported. The device includes a large amount of information with similar data grouped, and the groups are juxtaposed in order to facilitate pattern recognition and differentiation. This, in turn, facilitates visualization, retention, understanding, and use of the data presented. One sheet is placed over the other in order to visualize the mechanism between the substituted aromatic compound selected and the chosen reagent. It shows two aspects of EAS on separate pages and, then, demonstrates interactively how they interrelate. The two aspects are (1) the substitution itself, including the identity of the electrophile, the reagent(s) needed to generate it, and the substituent in the product and (2) the electronic effects of the groups in the aromatic compounds upon the intermediate(s) and the structure of the product. The effect of the use of the Electrophilic Aromatic Substitution Tool (also known as EAS-at-a-Glance) on the test performance of students enrolled in undergraduate organic chemistry was determined by a post-test-only control-group study. The subject samples were assigned to a control group and three device groups, differing with respect to use of the device. Results show that the EAS Tool enabled a better student performance (by 12.3% to 17.3%, depending upon the method of use), and that the best method of use is as an out-of-class supplement.