1,3-方酸衍生物亲电作用的理论研究

设计了负离子与2,4-二苯基-1,3-环丁烯二酮(Sq)的作用模型,用AM1方法研究了F^-,Cl^-,Br^-,O₂^-,S^2-等负离子与Sq的相互作用.结果表明,负离子对体系具有稳定化作用,离子电荷、离子极化性和取代基效应等对亲电作用有显著的影响.     

苯基在联苯亲电取代反应中的定位作用

运用G03程序,在HF/6-31G基组水平,分析了苯基（RPh）在联苯类化合物（RPh-Ph,R：NH2,CH3,OH,Br,H,CHO,CN,COOH,NO2）亲电取代反应中的定位作用。联苯和取代联苯的构象分析表明,联苯和间、对位取代联苯的碳-碳单键旋转的能垒很小,约12 kJ/mol,邻取代联苯的碳-碳单键旋转能垒△E（R）较大,且△E（COOH） > △E（NO2） > △E（CHO） > △E（CH3） > △E（NH2） > △E（OH） > △E（Br） > △E（CN）,因此,邻位取代基的空间效应较大,碳-碳单键旋转受阻。联苯和取代联苯的原子电荷分布随它们的构象改变而变化,在同一联苯或取代联苯化合物的最低能稳定结构中,无论取代基R为第一类还是第二类定位基,未取代苯环的碳原子总电荷密度比取代苯环碳原子的总电荷密度大,亲电取代反应将选择在未取代的苯环上发生;未取代苯环的邻位碳原子电荷密度较低、空间效应较大,而对位碳原子的电荷密度较大,亲电取代反应难以在该环的2,6-位（邻位）发生,将选择在该苯环的对位发生。因此,取代苯基（RPh-）在联苯的亲电取代反应中主要表现为对位定位基。     

Caveat receptor: proteomes on display

Display methods development is currently extending the application of this strategy beyond the generation of ligand binding reagents for research, clinical, or biotechnological purposes to its use as a primary research tool. Peptide- and cDNA display methods have the potential to contribute to understanding the mechanisms of certain classes of drugs and to help map protein-protein interactions of physiological importance. Although the critical contribution of comprehensive amino acid sequence databases has been recognized, of equal importance might be structural genomics concepts in the application of display system technology to proteomics research. Lessons learned from the study of antibody-antigen interactions are reviewed here and applied to the field of display technology with the goal of delineating major factors involved in the successful mimicry of natural protein-ligand interactions.     

Electrophilic Substitution in the Dihydroquercitin System. Aminomethylation

Treating dihydroquercetin with formaldehyde and amines under conditions of Mannich reaction provided mono- and diaminomethyl derivatives of dihydroquercetin.     

Aminomethyl psoralens. Electrophilic substitution of hydroxymethylphthalimide on linear furocoumarins

A new synthetic route to aminomethylpsoralens, substituted on the furan-ring, has been developed by electrophilic substitution of N-hydroxymethylphthalimide and subsequent hydrazinolysis. Hydroxy and methoxy activating functions on the psoralens lead to multi-site substitution and the products of these phthalimido-methylations resist simple cleavage with hydrazine. The two-step introduction of a single CH₂NH₂ group is successful in psoralens containing only methyl substituents.     

1,3-benzoxathioles. Electrophilic aromatic substitution

Some electrophilic substitution reactions on 1,3-benzoxathiole derivatives are described. Bromination and acylation reactions take place in position 5, i.e., para to the oxygen atom. 1,3-Benzoxathiole nitration yields a mixture of the corresponding sulfoxide and of the 6-nitro derivative when performed with 33% nitric acid, while, using a mixture of 40% nitric acid and acetic acid or acetyl nitrate, the 6-nitroderivative is obtained together with large amounts of gummy products. 2,2-Dimethyl-1,3-benzoxathiole nitration with 33% nitric acid yields disulfide XI, while with 33% nitric acid and acetic acid or with acetyl nitrate a mixture of disulfide XI and XII is obtained. The structure of the products have been determined by spectroscopic methods.     

α-Methylthiocarbonylation of Ketones. Generality and Regioselectivity

Over the past few years, there have been several methods documented for the preparation of β-keto thiolesters^2,3. However, most of these methods have limited synthetic applicability due to either the requirement of rather specific starting substrates³, or operational complexity, often coupled with unsatisfactory yields². A more promising procedure was briefly examined by Demuynck and Thuillier², who demonstrated the feasibility of β-keto thiolester formation by the reaction of an enolate ion with S,S'-dimethyl dithiocarbonate. Of the three simple acyclic ketones examined, products were obtained in moderate yields of 30–70%. In continuation of our investigation of the synthetic utility of β-keto thiolesters³ and efficient method of preparation was required. We have studied the α-methylthiocarbonylation process with special attention to its improvement, general applicability and regioslectivity.     

Electrophilic oxidant produced in the photodeoxygenation of 1,2-benzodiphenylene sulfoxide.

We report that the photodeoxygenation of 1,2-benzodiphenylene sulfoxide, 1, generates an intermediate capable of oxidizing the solvent benzene to phenol. The reactivity of the intermediate was probed with various substrates (2-methylbutane, chloride ion, and para-substituted aryl sulfides). The intermediate produced in the sulfoxide photodeoxygenation displays an electrophilic oxidation chemistry. Our data on 1 contrast with the behavior of hydroxyl radical but resemble the chemistry observed for gas-phase atomic oxygen [O((3)P)] and for solution-phase photodeoxygenations of dibenzothiophene sulfoxide, 3, and pyridine N-oxide, 5. Correlations are made between the ionization potential of the acceptor molecules and the logarithm of the relative rate constants in order to advance the idea that the oxidizing agent of the title reaction may be solution-phase O((3)P).     

论萘的亲电反应规律

辨析了“不能用计算化学方法解释萘的亲电反应规律”的观点 ,用半经验的量子化学计算方法 (EHMO)对萘分子进行了计算 ,证明这种计算方法能够解释萘的反应规律 ,并说明了电子效应和空间位阻效应对其亲电反应的影响。用同样的方法对菲分子也进行了计算     

Electrophilic addition to o-ArY-substituted phenylalkynes. A highly selective cyclization controlled by heteroatoms

Treatment of -(phenyloxy)phenylalkyne with HClO₄ or HBF₄ gave dibenz(b, f)oxepin , whereas the sulfur analogue, -(phenylthio)phenylalkyne , provided 1-phenyl-1-benzothiophenium salts .     

Electrophilic alkylation of fluoroolefins

Conclusions The electrophilic alkylation of fluoro-containing ethylenes by tert-butyl chloride and adamantane was accomplished.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1433–1434, June, 1978.The authors express their gratitude to P. V. Petrovskii for taking and interpreting the¹³C NMR spectra of (VIII).     

Electrophilic nitration of aromatics in ionic liquid solvents.

Potential utility of a series of 1-ethyl-3-methylimidazolium salts [emim][X] with X = OTf-, CF3COO-, and NO3- as well as [HNEtPri2][CF3COO] (protonated Hünig's base) ionic liquids were explored as solvent for electrophilic nitration of aromatics using a variety of nitrating systems, namely NH4NO3/TFAA, isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH, Cu(NO3)/TFAA, and AgNO3/Tf2O. Among these, NH4NO3/TFAA (with [emim][CF3COO], [emim][NO3]) and isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH (with [emim][OTf]) provided the best overall systems both in terms of nitration efficiency and recycling/reuse of the ionic liquids. For [NO2][BF4] nitration, the commonly used ionic liquids [emim][AlCl4] and [emim][Al2Cl7] are unsuitable, as counterion exchange and arene nitration compete. [Emim][BF4] is ring nitrated with [NO2][BF4] producing [NO2-emim][BF4] salt, which is of limited utility due to its increased viscosity. Nitration in ionic liquids is surveyed using a host of aromatic substrates with varied reactivities. The preparative scope of the ionic liquids was also extended. Counterion dependency of the NMR spectra of the [emim][X] liquids can be used to gauge counterion exchange (metathesis) during nitration. Ionic liquid nitration is a useful alternative to classical nitration routes due to easier product isolation and recovery of the ionic liquid solvent, and because it avoids problems associated with neutralization of large quantities of strong acid.     

含邻手性碳原子双键亲电加成反应的立体选择性模型

本文主要介绍了预测邻位具有手性中心π体系亲电加成反应的立体选择性模型,尤其是α,β-不饱和羰基化合物亲核共轭加成形成的烯醇负离子及其类似物和硝基烯烃亲核加成形成的氮酸根类中间体的烷基化和动力学控制质子化反应的立体选择性模型。立体位阻效应控制的Zimmerman前过渡态模型主要适用于底物构象受限的环状或联烯型烯醇负离子的动力学质子化。对于构象转化相对灵活的直链底物,Houk基于量子化学计算研究提出了亲电试剂的进攻角度或接触角在经过环状过渡态时是锐角还是钝角决定了亲电加成反应的立体选择性控制(Houk模型)。而Fleming模型首次将烯丙基A-1,3张力引入各类烯醇负离子烷基化和质子化的过渡态。Mohrig模型在考虑A-1,3张力的基础上,将吸电子取代基与即将形成的σ键反式共平面,主要阐述了立体电子效应对酯的烯醇负离子动力学控制质子化立体选择性的影响,后来又提出了金属离子参与的立体电子效应控制的六元环状半椅式模型。本文希望对理解亲电加成反应的立体化学控制提供一些有用的信息。     

Electrophilic Reactivities of Azodicarboxylates

The kinetics of the reactions of the azodicarboxylates 1 with the enamines 2 have been studied in CH₃CN at 20 °C. The reactions follow a second‐order rate law and can be described by the linear free energy relationship log k₂(20 °C)=s(N+E) (E=electrophilicity parameter, N=nucleophilicity parameter, and s=nucleophile‐specific slope parameter). With E parameters from ?12.2 to ?8.9, the electrophilic reactivities of 1 turned out to be comparable to those of α,β‐unsaturated iminium ions, amino‐substituted benzhydrylium ions, and ordinary Michael acceptors. While the E parameters of the azodicarboxylates 1 determined in this work also hold for their reactions with triarylphosphines, they cannot be used for estimating rate constants for their reactions with amines. Comparison of experimental and calculated rate constants for cycloadditions and ene reactions of azodicarboxylates provides information on the concertedness of these reactions.