Oxidative Coupling the Toluic Acid Dianion System

The behavior of all three toluic acid isomers upon treatment with two equivalents of base followed by the addition of iodine-containing reagents is described.     

Repairing the Thiol‐Ene Coupling Reaction

Thiol‐ene coupling (TEC) reactions emerged as one of the most useful processes for coupling different molecular units under reaction mild conditions. However, TEC reactions involving weak C? H bonds (allylic and benzylic fragments) are difficult to run and often low yielding. Mechanistic studies demonstrate that hydrogen‐atom transfer processes at allylic and benzylic positions are responsible for the lack of efficiency of the radical‐chain process. These competing reactions cannot be prevented, but reported herein is a method to repair the chain process by running the reaction in the presence of triethylborane and catechol. Under these reaction conditions, a unique repair mechanism leads to an efficient chain reaction, which is demonstrated with a broad range of anomeric O‐allyl sugar derivatives including mono‐, di‐, and tetrasaccharides bearing various functionalities and protecting groups.     

微波辐射-酶耦合催化(MIECC)反应

将微波辐射用于非水相酶催化可以获得很多有别于常规加热下的反应结果.本文讨论了微波的非热效应在酶促反应中的表现,探讨了微波辐射对酶的结构、构象、活性及酶催化反应动力学的影响,以及微波辐射-酶耦合催化对反应的对映选择性、底物专一性、前手性选择性和区域选择性的影响.在大多数场合,适当的微波辐射不会损伤酶活而且可以提高反应速率,而对酶特异性的影响则不一而论.     

胺作为配体在钯催化偶联反应中应用

对近期我们研究小组及其它研究小组在利用胺作为钯催化偶联反应的配体研究进展进行了总结. 钯/胺作为催化体系主要应用的偶联反应包括: Suzuki-Miyaura交叉反应, Sonogashira交叉反应, Stille交叉反应, Hiyama交叉反应和Heck反应. 研究结果表明胺可以作为价廉和高效的配体促进钯催化交叉偶联反应.     

Visible-Light Photocatalysis of the Ketyl Radical Coupling Reaction

Ketyl radical coupling reactions for the construction of diversely functionalized alcohols have been continuously developed for many decades. Based on the recently widespread application of photocatalysis, ketyl radical coupling reactions have also witnessed rapid development. This Minireview aims to briefly and concisely summarize the methods to construct ketyl radical intermediates through visible-light photocatalysis over the past 10 years. The ketyl-radical-generation activators are grouped as Lewis acids, Brønsted acids, in situ generated Brønsted acids, and others.     

微波辐射-酶耦合催化(MIECC)反应

将微波辐射用于非水相酶催化可以获得很多有别于常规加热下的反应结果。本文讨论了微波的非热效应在酶促反应中的表现,探讨了微波辐射对酶的结构、构象、活性及酶催化反应动力学的影响,以及微波辐射-酶耦合催化对反应的对映选择性、底物专一性、前手性选择性和区域选择性的影响。在大多数场合,适当的微波辐射不会损伤酶活而且可以提高反应速率,而对酶特异性的影响则不一而论。     

Coupling NMR to NOM

This work itemizes and critically assesses several 1D and multi-dimensional nuclear magnetic resonance (NMR) techniques, in both the liquid (solvent suppression, APT, DEPT, INEPT, COSY, TOCSY, HSQC, HMQC, HMBC, NOESY, ROESY and others) and solid states (DP, SACP, RAMP-CP, CP-TOSS, MQ-DEPT, 2D ¹H–¹³C HETCOR and others), which are relevant to the characterization of natural organic matter (NOM). The pros and cons of many of the discussed techniques are compared in an effort to provide guidance to the most beneficial utilization of these NMR instrumental techniques for researchers interested in gaining insight into various aspects of NOM.Abbreviations 1D One dimensional - 2D Two dimensional - APT Attached proton test - BIRD Bilinear rotation decoupling - CP Cross polarization - COSY Correlation spectroscopy - CSA Chemical shift anisotropy - DEPT Distortionless enhancement by polarization transfer - DMSO Dimethyl sulfoxide - DOSY Diffusion ordered spectroscopy - DP Direct polarization - DQ Double quantum - FID Free induced decay - FT Fourier transform - FT-ICR-MS Fourier transform-ion cyclotron resonance-mass spectroscopy - HETCOR Heteronuclear correlation - HH Hartmann–Hahn - HMBC Heteronuclear multiple bond correlation - HMQC Heteronuclear multiple quantum coherence - HSQC Heteronuclear single quantum coherence - INEPT Insensitive nuclei enhanced by polarization transfer - LR-COSY Long-range COSY - MAS Magic-angle spinning - MQ Multiple quantum - MS Mass spectroscopy - NMR Nuclear magnetic resonance - NOE Nuclear Overhauser enhancement - NOESY Nuclear Overhauser enhanced spectroscopy - NOM Natural organic matter - PASS Phase adjustment of spinning sidebands - RAMP Ramped amplitude - RESTORE Restoration of spectra via T _CH and T one rho (T _1H) editing - r.f. Radio frequency - ROESY Rotating frame Overhauser enhancement spectroscopy - SACP Single amplitude cross polarization - SOM Soil organic matter - SS Spinning sideband - TMS Tetramethylsilane - TOCSY Total correlation spectroscopy - TOSS Total suppression of sidebands - TPPM Two-pulse phase modulation - VCT Variable contact time - VSL Variable spin lock - WATERGATE Water suppression by gradient tailored excitation     

Coupling constants in the direct configuration interaction method

A general algorithm of evaluation of the coefficients of molecular integrals (coupling constants) appearing in the direct configuration interaction method is derived. The configurations are assumed to be spin-adapted antisymmetrized products of orthonormal orbitals. No limitation is imposed either upon the reference state (the number of the singly occupied orbitals may be arbitrary) or upon the excitation multiplicity.     

Ni催化的Suzuki偶联反应

本文主要对Ni催化的Suzuki偶联反应的发展历程和近年来碳卤键断裂类、碳氧键断裂类、碳碳键断裂类、碳氮键断裂类和碳硫键断裂类Ni催化Suzuki偶联反应进行总结。通过近十年研究,各类新型催化剂、配体、添加剂不断被开发,使反应活性大为提高,反应条件越来越温和。对目前认为Ni催化的Suzuki偶联反应的机理进行了梳理,发现Ni催化的Suzuki偶联反应催化剂循环方式有两种,即Ni(0)/Ni(Ⅱ)循环和Ni(Ⅰ)/Ni(Ⅲ)循环。因此,本文认为研究和发展价廉的金属Ni催化剂是研究Suzuki偶联反应的一个重要方向,未来Ni催化Suzuki偶联反应的研究将会集中在机理探究、新型催化剂和配体设计、多类型碳碳键构建(Csp~2-Csp~3、Csp~3-Csp~3)以及广泛底物的不对称Ni催化的Suzuki偶联反应。     

基于环糊精和富勒烯偶联体系的新型分子机器*

超分子化学是当前研究热点领域之一,利用超分子体系来模拟宏观过程,进而将宏观机器纳米尺寸化更是备受瞩目。环糊精与富勒烯各自具有非常优良的性质,而基于环糊精和富勒烯偶联体系的新型“加工型”分子机器,与传统的“运动型”分子机器不同,不是强调分子间与分子内的位置变化,而是强调对特定客体分子“识别-捕捉-加工-释放”的过程。这种新型的分子机器将为包括生物酶模拟、生物过程研究、光能固定等领域的研究提供新思路。本文综述了环糊精和富勒烯偶联体系的研究进展：首先介绍了不同种类的环糊精和富勒烯偶联体系的合成,包括合成思路、步骤方法及表征;然后叙述了此体系的应用领域,包括分子识别、DNA裂解、电子传输等方面;最后结合现阶段的研究状况,对其发展前景进行了展望。     

Stille偶联法合成芳基取代联吡啶衍生物

以2-溴吡啶为原料,采用碘化和Halogen-Dance反应一锅法合成了2-溴-4-碘吡啶,产率提高至65%.利用卤素反应活性的差异,通过选择性Kumada偶联反应方便地合成了2-溴-4-(4-甲基)苯基吡啶,并通过Stille偶联反应合成了一系列二联、三联及四联吡啶,进行了NMR、MS、IR以及元素分析等表征.     

Hierarchy in the Halogen Activation During Surface-Promoted Ullmann Coupling

Within the collection of surface-supported reactions currently accessible for the production of extended molecular nanostructures under ultra-high vacuum, Ullmann coupling has been the most successful in the controlled formation of covalent single C−C bonds. Particularly advanced control of this synthetic tool has been obtained by means of hierarchical reactivity, commonly achieved by the use of different halogen atoms that consequently display distinct activation temperatures. Here we report on the site-selective reactivity of certain carbon-halogen bonds. We use precursor molecules halogenated with bromine atoms at two non-equivalent carbon atoms and found that the Ullmann coupling occurs on Au(111) with a remarkable predilection for one of the positions. Experimental evidence is provided by means of scanning tunneling microscopy and core level photoemission spectroscopy, and a rationalized understanding of the observed preference is obtained from density functional theory calculations.     

Theoretical Study on the Mechanism of Sonogashira Coupling Reaction

The mechanism of palladium-catalyzed Sonogashira cross-coupling reaction has been studied theoretically by DFT （density functional theory） calculations. The model system studied consists of Pd（PH3）2 as the starting catalyst complex, phenyl bromide as the substrate and acetylene as the terminal alkyne, without regarding to the co-catalyst and base. Mechanistically and energetically plausible catalytic cycles for the cross-coupling have been identified. The DFT analysis shows that the catalytic cycle occurs in three stages： oxidative addition of phenyl bromide to the palladium center, alkynylation of palladium（Ⅱ） intermediate, and reductive elimination to phenylacetylene. In the oxidative addition, the neutral and anionic pathways have been investigated, which could both give rise to cis-configured palladium（Ⅱ） diphosphine intermediate. Starting from the palladium（Ⅱ） diphosphine intermediate, the only identifiable pathway in alkynylation involves the dissociation of Br group and the formation of square-planar palladium（Ⅱ） intermediate, in which the phenyl and alkynyl groups are oriented cis to each other. Due to the close proximity of phenyl and alkynyl groups, the reductive elimination of phenylacetylene proceeds smoothly.     

Comparison of Oxidative Aromatic Coupling and the Scholl Reaction

Does the dehydrogenative coupling of aromatic compounds mediated by AlCl₃ at high temperatures and also by FeCl₃, MoCl₅, PIFA, or K₃[Fe(CN)₆] at room temperature proceed by the same mechanism in all cases? With the growing importance of the synthesis of aromatic compounds by double C? H activation to give various biaryl structures, this question becomes pressing. Since some of these reactions proceed only in the presence of non‐oxidizing Lewis acids and some only in the presence of certain oxidants, the authors venture the hypothesis that, depending on the electronic structure of the substrates and the nature of the “catalyst”, two different mechanisms can operate. One involves the intermediacy of a radical cation and the other the formation of a sigma complex between the acid and the substrate. The goal of this Review is to encourage further mechanistic studies hopefully leading to an in‐depth understanding of this phenomenon.     

An Iodide-Mediated Anodic Amide Coupling

The ubiquity of amide bonds, present in natural products and common pharmaceuticals renders this functional group one of the most prevalent in organic chemistry. Despite its importance and a wide variety of existing methods for its formation, the latter still can be a challenge for classical activating reagents such as chloridating agents or carbodiimides. As the spent reagents often cannot be recycled, the development of more sustainable methods is highly desirable. Herein, we report an operationally simple and mild indirect electrochemical protocol to effect the condensation of carboxylic acids with amines, forming a wide variety of carboxamides.     

Light-Driven Enantioselective Carbene-Catalyzed Radical-Radical Coupling

An enantioselective carbene-catalyzed radical-radical coupling of acyl imidazoles and racemic Hantzsch esters is disclosed. This method involves the coupling of an N-heterocyclic carbene-derived ketyl radical and a secondary sp³-carbon radical and allows access to chiral α-aryl aliphatic ketones in moderate-to-good yields and enantioselectivities without any competitive epimerization. The utility of this protocol is highlighted by the late-stage functionalization of various pharmaceutical compounds and is further demonstrated by the transformation of the enantioenriched products to biologically relevant molecules. Computational investigations reveal the N-heterocyclic carbene controls the double-facial selectivity of the ketyl radical and the alkyl radicals, respectively.     

Coupling Interactions between Sulfurous Acid and the Hydroperoxyl Radical

Radical–molecule complexes associated with the hydroperoxyl radical (HOO) play an important role in atmospheric chemistry. Herein, the nature of the coupling interactions between sulfurous acid (H₂SO₃) and the HOO radical is systematically investigated at the B3LYP/6‐311++G(3df,3pd) level of theory in combination with the atoms in molecules (AIM) theory, the natural bond orbital (NBO) method, and energy decomposition analyses (EDA). Eight stable stationary points possessing double H‐bonding features were located on the H₂SO₃???HOO potential energy surface. The largest binding energies of ?12.27 and ?11.72 kcal mol^?1 are observed for the two most stable complexes, where both of them possess strong double intermolecular H‐bonds of partially covalence. Moreover, the characteristics of the IR spectra for the two most stable complexes are discussed to provide some help for their possible experimental identification.     

钯和四齿膦配体催化剂应用于Heck反应的研究

设计合成了以联萘二胺为骨架的四齿膦配体N,N,N',N'-四(二苯基膦甲基)-(1,1'-联萘)-2,2'-二胺,并将其与钯组成的催化体系用于苯乙烯和芳卤的Heck反应,该催化体系对各种卤代芳烃都表现出了很高的催化活性.对活化底物对溴苯腈,即使底物与催化剂的物质的量比达到10 000,反应20 h几乎能达到定量转化;该催化体系对活性更低的杂环底物也取得了良好的催化效果.     

多场耦合作用下光热敏感介电凝胶的力电耦合变形行为

介电弹性体在电场作用下将产生形变,为获得高的变形能,需对介电弹性体施以较强的电场,而强电场的施加可能诱发力电耦合失稳导致失效。针对光热敏感介电凝胶力电耦合变形行为,基于热力学和连续介质力学理论建立力电耦合变形模型,分析了光强、温度以及预拉伸对光热敏感介电凝胶力电耦合变形行为的影响,结果表明:无预拉伸时,随着电场强度的增大,光热敏感介电凝胶最终发生力电失稳,光强越小、温度越低发生力电失稳时的临界电压越高;预拉伸可显著改善力电稳定性,施加等双轴预拉伸后,凝胶厚度方向的伸长率显著变小,电场强度随电位移增大而线性增大,未出现力电失稳现象。