金属锌在有机合成反应中的应用

综述了近年来以金属锌作为还原剂的各种反应，以及它在有机合成中的应用。 讨论了金属锌在催化剂的作用下，还原碳碳、碳氮、碳氧重键及碳氧、碳硫、碳卤 等单键的还原和偶联。     

碳质表面异相还原NO2的反应机理

基于量子化学密度泛函理论（DFT），研究了碳质表面异相还原NO₂的反应机理，针对Zigzag与Armchair两种碳质表面，采用M06-2X方法与6-311G （d）基组联用，优化得到了不同反应路径下所有驻点的几何构型与能量，并对各路径进行了热力学与动力学分析，重点探究了CO在NO₂异相还原反应中的作用规律，同时考察了碳质表面与反应温度对异相反应的影响。计算结果表明，NO₂在碳质表面的异相还原过程主要分为两个阶段，即NO₂还原阶段与碳氧化物释放阶段。通过对比无CO分子参与的反应可知，参与反应的CO分子可以降低各阶段的反应能垒并且加快各阶段的反应速率；CO分子存在时，NO₂还原阶段的反应能垒被降低，促进了NO₂还原成NO的异相反应过程，同时参与反应的CO分子与碳质表面剩余氧原子结合，形成CO₂分子并释放，使碳氧化物释放阶段的反应能垒降低，从而促进了整体还原反应的进行。此外，与Armchair型相比，基于Zigzag型碳质表面的NO₂异相还原反应能垒更低且反应速率更快，说明NO₂异相还原反应更容易在Zigzag型碳质表面进行。最后，由反应动力学分析可知，随着温度上升，各阶段的反应速率均增大，说明提高温度对碳质表面的NO₂异相还原能够起到促进作用。     

光催化有机物偶联/芳构化放氢反应研究进展

光催化氧化还原反应具有绿色、高效、安全等优势,已经在有机化学中得到广泛关注.介绍了基于光催化的偶联/芳构化放氢反应,通过使用光催化剂/催化剂的双催化体系,可用于光催化有机碳-碳和碳-杂原子成键反应,且反应中氢气是唯一的副产物.强调了有机光氧化还原体系的构建与催化机理.     

有机硒,碲化合物在高选择性合成反应中的应用

综述了有机硒，碲化合物的合成及其在高选择性合成反应中的反应。低价硒，碲化合物具有良好的还原选择性，可用于多种碳－氢键的形成，硫叶立德和α－芳硒基取代的胂叶立行署中发生Ｗｉｔｔｉｇ型反应，是形成碳－碳双键的重要方法。     

玻碳电极上DTAB对氧还原反应的促进作用

用旋转圆盘玻碳电极研究了阳离子表面活性剂十二烷基三甲基溴化铵(DTAB)对氧还原反应的影响. 结果表明, DTAB明显提高了玻碳电极对氧还原的电催化活性. 通过对氧还原电流与旋转速度的关系以及动力学电流与电位的Tafel关系分析, 发现DTAB提高了玻碳电极对氧还原反应电荷传递步骤的传递系数, 因此加快了氧还原的动力学过程.     

碳基无金属氧还原电催化剂研究的新进展

以替代铂为目标的高性能廉价氧还原电催化剂的研究为当今科学前沿. 近年来人们发现, 掺杂的碳基纳米结构具有催化活性高、稳定性好、资源丰富、抗CO和抗甲醇能力强等优点, 是一种新型无金属氧还原电催化剂, 具有替代铂基催化剂的潜力. 本文结合作者课题组的最新研究成果, 简要综述了碳基无金属氧还原电催化剂研究的主要进展, 重点关注了富电子氮和缺电子硼单/共掺杂的碳纳米结构的氧还原催化性能及其与电子结构的关系, 展望了碳基无金属氧还原催化剂的发展策略与前景.     

碳催化剂在催化反应中的应用

由于碳材料表面存在缺陷,可生成具有不同性能的活性位,因此可催化不同的热催化反应.我们首先介绍了单质碳材料的表面结构化学:其表面活性位主要为含杂原子官能团;然后对其可催化的反应进行了介绍:碳单质材料可催化选择性氧化反应、高级氧化反应、还原反应、烷烃活化反应、酸催化反应、电催化还原和氧化反应等.对碳单质催化剂的制备方法、所...     

基于煤气化细渣构建碳基氧还原催化剂及其催化性能研究

气化细渣是煤气化过程产生的一种含碳量较高的固体废弃物。经炭灰分离得到的高炭是制备炭材料的潜在碳源。本研究以气化细渣浮选-酸洗后的高炭为前驱体，通过高温活化制备了氮掺杂碳基催化剂，结合拉曼光谱、XPS和SEM等表征，探究了活化剂比例和氮源对催化剂理化特性的影响，揭示了两者与催化剂氧还原性能的内在关联，验证了气化细渣作为原料制备碳基氧还原催化剂的可行性。结果表明，随着活化剂KOH比例的增加，碳基催化剂的氧还原催化性能先增加后减小，当高炭和KOH质量比为1∶4时其催化性能最优。此外，相较于氯化铵，以三聚氰胺作为氮源具有更强的氮掺杂效应，使得CKN₆-143催化剂的起始电位可达0.87 V（vs. RHE），极限扩散电流密度为4.95 mA/cm²，平均电子转移数为3.82，表现出良好的电催化性能，为气化细渣的高值化利用奠定了基础。     

过氧化钠与氢气和炭发生氧化还原反应的实验设计

设计探究过氧化钠能否与氢气、碳发生氧化还原反应的实验。实验证明：过氧化钠与氢气反应生成氢氧化钠,与炭粉反应生成碳酸钠和氧化钠。     

希夫碱在有机合成中的应用研究

简要评述了近十年来，希夫碱作为底物，在不对称催化氢化，不对称还原、氧 化，α－碳不对称烷基，[4＋2]、[3＋2]和[2＋2]环加成以及与Lawessen试剂等反 应的应用性研究进展。     

Recent topics of the natural product synthesis by Horner–Wadsworth–Emmons reaction

The Horner–Wadsworth–Emmons (HWE) reaction has become well established among existing methodologies for the highly stereoselective olefination of carbonyl compounds. The reliability of this reaction in terms of its robustness, high stereoselectivity, and broad substrate scope permit retrosynthetic disconnection of the olefin bond in α,β-unsaturated carbonyl intermediates in natural product synthesis. This review discusses recent applications of the HWE reaction in natural product synthesis, highlighting its use for carbon chain elongation, coupling reactions of synthetic segments, ring-closing reactions, tandem reactions including HWE olefination, and asymmetric reactions.     

Coordination of Lewis acid to eta(2)-enonepalladium(0) leading to continuous structure variation from eta(2)-olefin type to eta(3)-allyl type.

The reaction of alpha,beta-unsaturated carbonyl compounds, a palladium(0) complex, and Lewis acids led to the formation of a new class of complexes showing a wide variety of structures with eta(2)-type and eta(3)-type coordination of the carbonyl compounds. The reaction of Pd(PhCH=CHCOCH(3))(PPh(3))(2) with BF(3).OEt(2) or B(C(6)F(5))(3) quantitatively gave palladium complexes 1a,b having BX(3)-coordinated eta(2)-enonepalladium structure, as revealed by X-ray structure analysis of the B(C(6)F(5))(3) adduct 1b. On the other hand, the reaction of Pd(PhCH=CHCHO)(PPh(3))(2) with BF(3).OEt(2) or B(C(6)F(5))(3) gave distorted zwitterionic eta(3)-allylpalladium complexes 3a,b, where the Pd-carbonyl carbon distance in 3a (2.413(4) A) is much shorter than that (2.96(1) A) in 1b. The values of the P-P coupling constant and (13)C chemical shift for carbonyl carbon are useful criteria for predicting how the eta(3)-coordination mode contributes to the structure of the enone-palladium-Lewis acid system. Molecular orbital calculations on the series of model complexes suggest that orbital overlap in the highest occupied molecular orbital between the palladium and carbonyl carbon is enlarged by coordination of the Lewis acid to the carbonyl group. Palladium-catalyzed conjugate addition of R-M (R-M = AlMe(3), AlEt(3), ZnEt(2)) and its plausible reaction path are also reported.     

Synthèse domino du noyau tricyclique ABC de strigolactones et analogues

The diversity-oriented synthesis of the ABC tricyclic core of strigolactones and analogues is described starting from ortho-halogenated aromatic or vinylic carbonyl compounds and dimethyl itaconate. It involves a conjugate addition/aldol coupling/lactonization domino process that allows the formation of three carbon–carbon bonds in a single experimental step. Functional group interconversions as well as a putative reaction mechanism are presented.     

Catalytic asymmetric Henry reaction

The classical Henry reaction, the coupling of a nitroalkane with a carbonyl compound in the presence of a base, is an important C–C bond forming reaction in organic chemistry giving β-nitroalcohols, which are useful synthons in organic synthesis. However, an asymmetric version of the reaction, that has been developed recently, gives a new dimension to the classical Henry reaction whereby the control of stereochemistry of two newly generated carbon centres has become possible. In this review, the various catalytic methods for this purpose are discussed.     

单取代芳烃对位选择性碳氢活化反应研究

以单取代芳烃为芳基化试剂,以羰基为导向定位基团,研究了单取代芳烃对位选择性与芳香酮的交叉脱氢偶联反应。该方法的高选择性一方面体现在用作芳基化试剂的单取代芳烃能够单一选择性地发生对位碳氢活化,并生成对位取代产物;另一方面,作为弱导向基团的羰基具有优异的邻位导向定位作用,高选择性地发生羰基邻位碳氢键活化。此外,该方法还具有反应条件温和、反应效率高、底物范围广、氧化剂廉价易得等优点,为对位取代联芳基化合物的合成提供了一条切实可行的途径。     

Oxovanadium(V)-Catalyzed Deoxygenative Coupling Reaction of Alcohols with Trimethylsilyl Enol Ethers in the Presence of MS3A

Oxovanadium(V)-catalyzed deoxygenative coupling reaction of allyl alcohols with trimethylsilyl enol ethers was demonstrated to afford γ,δ-unsaturated carbonyl compounds in one-step. The catalytic deoxygenative coupling reaction of allyl alcohols proceeded smoothly with both aromatic and aliphatic trimethylsilyl enol ethers. This catalytic deoxygenative coupling system could be applied to the deoxygenative coupling reaction of benzyl alcohols with trimethylsilyl enol ethers, providing the corresponding carbonyl compounds. Furthermore, a gram-scale catalytic synthesis of the γ,δ-unsaturated carbonyl compound was successfully performed to validate the scalability of this catalytic deoxygenative coupling reaction.     

Transition‐Metal‐Free Formal Sonogashira Coupling and α‐Carbonyl Arylation Reactions

Transition‐metal‐free formal Sonogashira coupling and α‐carbonyl arylation reactions have been developed. These transformations are based on the nucleophilic aromatic substitution (S_NAr) of β‐carbonyl sulfones to electron‐deficient aryl fluorides, producing a key intermediate that, depending on the reaction conditions, gives the aromatic alkynes or α‐aryl carbonyl compounds. The development of these reactions is presented and, based on investigations under basic and acidic conditions, mechanisms have been proposed. To develop the formal Sonogashira coupling further, a milder, two‐step protocol is also disclosed that expands the reaction concept. The scope of these reactions is demonstrated for the synthesis of Sonogashira and α‐carbonyl arylated products from a range of electron‐deficient aryl fluorides with a variety of functional groups and aryl‐, heteroaryl‐, alkyl‐, and alkoxy‐substituted sulfone nucleophiles. These transition‐metal‐free reactions complement the metal‐catalyzed versions in terms of substitution patterns, simplicity, and reaction conditions.     

Nickel-catalyzed cycloadditions of unsaturated hydrocarbons, aldehydes, and ketones

The nickel-catalyzed cycloaddition of unsaturated hydrocarbons and carbonyls is reported. Diynes and enynes were used as coupling partners. Carbonyl substrates include both aldehdyes and ketones. Reactions of diynes and aldehydes afforded the [3,3] electrocyclic ring-opened tautomers, rather than pyrans, in high yields. The cycloaddition reaction of enynes and aldehydes afforded two distinct products. A new carbon-carbon bond is formed, prior to a competitive beta-hydrogen elimination of a nickel alkoxide, between the carbonyl carbon and either one of the carbons of the olefin or the alkyne. The steric hindrance of the enyne greatly affected the chemoselectivity of the cycloaddition of enynes and aldehydes. In some cases, dihydropyran was also formed. The scope of the cycloaddition reaction was expanded to include the coupling of enynes and ketones. No beta-hydrogen elimination was observed in cycloaddition reaction of enynes and ketones. Instead, C-O bond-forming reductive elimination occurred exclusively to afford dihydropyrans in excellent yields. In all cases, complete chemoselectivity was observed; only dihydropyrans where the carbonyl carbon forms a carbon-carbon bond with a carbon of the olefin, rather than of the alkyne, were observed. All cycloaddition reactions occur at room temperature and employ nickel catalysts bearing the hindered 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or its saturated analogue, 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazolin-2-ylidene (SIPr).     

A study of NMR parameters of cyclobutenones and benzocyclobutenones

An NMR study of ketones 5–12 was undertaken to gain insight into the low electrophilicity of the carbonyl moiety of butenones 9–11. Initial IR studies on compounds 9–12 indicated that there is relatively strong double bond character (and hence low electrophilicity) in the carbonyl of saturated and unsaturated cyclobutyl ketones. The ¹³C chemical shifts confirm that the carbonyl moiety is highly conjugated with the fused benzene ring in 9, and with the olefinic linkage in 10 and 11. Partial positive charge is distributed away from the carbonyl carbon, which is also expected to lower the electrophilicity of the carbonyl carbon atoms of 9–11. One‐bond carbon–proton coupling constants (¹J_CH) depend directly on carbon hybridization. In the four‐membered ring ketones 9–12 the experimental values are larger than in cyclobutane, probably as a result of the additional strain of the extra trigonal centers in the ring. A similar trend is seen in the case of the olefinic CH in 10 and 11 (ca 175 Hz), for which the coupling constant is larger than for the corresponding carbon in cyclobutene. ¹J_CC values between the ring carbon atoms of the cyclobutenones are some 20% lower than in the models—a bigger difference than in cyclobutanes, again indicative of the increased ring strain. The very low 42.4 Hz coupling between C‐1 and C‐2 in 9 might well indicate a measure of bond localization. ²J_CC and ³J_CC values are also discussed. Copyright © 2003 John Wiley & Sons, Ltd.