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开发了一种由金和钯催化π-活化由炔醇合成呋喃衍生物的集成方法.该合成策略是最显著的特点适用于带环辛基的底物,其适用范围比之前报道的有很大扩展.在Sonogashira反应条件下,由相应底物可直接得到环辛基呋喃.Pd在这些反应中起到2个重要作用:底物发生偶联反应的关键催化剂;通过π-活化促进炔醇中间体成环反应.该方法在一步合成3-碘呋喃反应中作用很突出,使通过偶联法进一步官能团化成为可能.我们还将AuBr_3用于多米诺成环/C-H键活化反应和无环前体的成环反应.本文结果表明,在该类成环反应中金和钯催化剂相辅相成. 相似文献
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噁唑/噁唑啉骨架广泛存在于天然产物和合成生物活性分子中,备受到化学工作者的关注[1].在众多合成方法中,炔丙基酰胺的分子内环化反应被认为是合成1,3-噁唑衍生物最直接和最具原子经济性的途径(Scheme 1,path a).反应的催化剂可以是酸、碱或过渡金属,如金、银、钯和铜等[2].其中Au配合物作为一类重要的软金属催化剂,能够有效活化碳碳叁键。 相似文献
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对钯催化的Grignard类型反应作了论述.总结了钯催化的有机卤化物或炔烃与C=O键或C≡N键的二组分反应和有机卤化物、烯烃或炔烃与C=O键或C≡N键的三组分反应.在这些反应中的C-Pd键是通过C-X键与Pd(0)的氧化加成或通过碳碳双键或叁键的碳/亲核钯反应生成,C-Pd键与C=O键或C≡N键之间的反应一般为分子内反应.当然,人们也观察到了通过芳香C-H键活化产生的芳基碳钯键与腈基的分子间反应.在这些反应中催化剂的再生是关键.本工作对反应的机理也作了一些探讨. 相似文献
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Pd催化的配体导向C-H键官能化反应已经成为有机化学中一种重要的合成手段. 我们用B3PW91密度泛函方法研究了Pd催化的配体导向C-H键乙酰化反应中催化剂和底物配合步骤以及C-H键活化步骤中的热力学性质. 研究发现, 具有不同导向基团的反应物之间竞争反应的选择性取决于导向基团与Pd(OAc)2的配合步骤, 配合反应稳定常数大的较容易生成乙酰化的产物. 另一方面, 反应的选择性与C-H键的活化步骤无关, 并且与导向基团的配位原子的气相碱性、原子上的电荷密度以及最高占据轨道能量都没有相关性. 相似文献
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C-H键活化是近年来发展最为迅速的研究领域之一,从自然界中广泛存在C-H键的简单底物为原料,利用C-H键直接活化策略来构建高附加值的化学品是一类具有高原子经济性的化学反应.然而,由于C-H键的稳定性使得C-H键的选择性官能团化过程具有极大的挑战.例如,烃类化合物的C-H选择性氧化生成醇/酮化合物在C1化学以及有机合成反应中占据重要地位,同时C-H键的高解离能以及氧化试剂的高活性往往使得这类反应的选择性难以调控.近日,中科院大连化学物理研究所张涛和王爱琴领导的团队在脂肪族、芳香族烃类化合物的C-H选择性氧化反应中取得新的研究进展.作者使用Fe-N-C单原子催化剂,化学计量的叔丁基过氧化氢为氧化剂,在室温条件下实现了烃类化合物的选择性氧化反应,一系列底物包括带有吸电子基团的硝基(-NO_2)、供电子基团的甲氧基(-OCH_3)、杂环化合物以及脂肪族化合物(环己烷)均可以高选择性(98%)实现转化.事实上,Fe-N-C单原子催化剂的活性与选择性可与均相催化剂([Cu((R,R)-BPBP)]+)相媲美,同时该催化剂在绿色水溶剂中表现出优异的循环稳定性.这项工作的另一个意义在于建立起多相催化领域中活性位点与反应性能之间的构效关系.通过HAADF-STEM,XPS,XAS,ESR及穆斯堡尔谱等表征手段,清楚地证明Fe-N-C催化剂中三价铁离子存在多种配位结构(FeN_x,x=4,5,6),催化剂活性与Fe-Nx的特定结构密切关联.C-H键选择性氧化反应的最高活性位点为中自旋FeN_5位点,其活性高出低自旋/高自旋的FeN_6位点一个数量级,是FeN_4位点活性的3倍之多.而该FeN_5结构的数量在Fe-N-C-700的单原子催化剂上仅占18%,说明Fe-N-C催化剂的活性具有很大的提升空间.文中报道的Fe-N_x-C催化剂可被认为是一类新型的单原子催化剂,其中,N_x基团为一种强有力的配体.由于单原子催化剂兼具均相催化剂孤立均一的活性位点及多相催化剂易于循环使用的优势,单原子催化剂有望成为连接均相催化与非均相催化的桥梁.目前,单原子催化剂已成为多相催化领域一个新的研究热点与前沿.这篇工作中的FeN_5位点与血红蛋白的Fe中心结构类似,从这个角度出发,FeN_5位点为连接酶催化剂与多相单原子催化剂提供了一个很好的案例.然而,FeN_5位点周围环境的细微变化都会直接影响其反应活性以及选择性,从而导致多相催化中的FeN_5具有较差的O_2活化能力.因此,设计更为高效的多相单原子催化剂,实现类似于酶催化中高效高选择性地活化底物分子,仍然具有很大的挑战与空间. 相似文献
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Prof. Dr. Jie-Ping Wan Zhi Tu Yuyun Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(28):6907-6910
A transient and recyclable C−H iodination has been designed for the synthesis of isoflavonoids through the domino reactions of o-hydroxyphenyl enaminones and aryl boronic acids in the presence of catalytic KI and Pd catalyst. Instead of the conventional cross-coupling strategy employing pre-halogenated substrates, this method transforms raw C−H bond by means of a transient C−H halogenation to smoothly relay the subsequent C-arylation. Consequently, such a method avoids the pre-functionalization for C−halogen bond installation as well as the generation of stoichiometric halogen-containing waste following the cross-coupled product, disclosing an intriguing new coupling protocol to forge the C−C bond in the virgin area between classical C−X (X=halogen) bond cross coupling and the C−H activation. 相似文献
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Alessio Baccalini Prof. Giuseppe Faita Prof. Giuseppe Zanoni Prof. Debabrata Maiti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):9749-9783
Sequential, domino and tandem reactions could be defined as a sequence of synthetic transformations that occur one after the other, in the same reaction flask. This Review highlights recent advances at the overlap of two worlds: transition-metal mediated C−H activation as a trigger of cascade reaction, for the heterocycles synthesis. To shed some light on this intricate “middle-earth”, focus was put on the reaction mechanism rather than the type of metal or the chronological order of the reaction. The aim is to separate, and then highlight, the true domino reactions initiated by C−H activation, compared to other examples of C−H functionalization for heterocycle syntheses. 相似文献
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采用密度泛函理论方法在B3LYP/6-31G(d)水平上对吡啶二硫代酯与丁二烯的杂Diels-Alder反应的反应机理进行了理论计算研究, 并且也考虑了催化效应、溶剂化效应及取代基效应对反应机理和反应位垒的影响. 结果表明, 这些反应均以协同非同步的方式进行. 在大多数反应中, C—S键先于C—C键形成; 而在少数几个反应中, 则是C—C键先于C—S键形成. 催化剂和三甲基硅氧基取代基能通过改变反应物分子的前线轨道能级来降低反应的活化位垒. 溶剂只对涉及到离子物种的H+催化反应的势能剖面有明显影响. 对于BF3催化的吡啶二硫代酯与1-三甲基硅氧基丁二烯的反应, 计算结果不仅正确预测了实验所发现的完全的区域选择性和较高的立体选择性, 而且表明这些结果很可能是由于在两个过渡态中存在C—H…F氢键相互作用造成的. 相似文献
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Copper‐Catalyzed Domino Synthesis of 2‐Imino‐1H‐imidazol‐5(2H)‐ones and Quinoxalines Involving CC Bond Cleavage with a 1,3‐Dicarbonyl Unit as a Leaving Group 下载免费PDF全文
Yan Yang Fan Ni Wen‐Ming Shu Prof. An‐Xin Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11776-11782
Although 2‐imino‐1H‐imidazol‐5(2H)‐ones have important biological activities in metabolism, their synthesis has rarely been investigated. Quinoxalines as “privileged scaffolds” in medicinal chemistry have been extensively investigated, but the development of novel and efficient synthetic methods remains very attractive. Herein, we have developed two copper‐catalyzed domino reactions for the synthesis of 2‐imino‐1H‐imidazol‐5(2H)‐ones and quinoxalines involving C?C bond‐cleavage with a 1,3‐dicarbonyl unit as a leaving group. The domino sequence for the synthesis of 2‐imino‐1H‐imidazol‐5(2H)‐ones includes aza‐Michael addition, intramolecular cyclization, C?C bond‐cleavage, 1,2‐rearrangement, and aerobic dehydrogenation reaction, whereas the domino sequence for the synthesis of quinoxalines includes aza‐Michael addition, intramolecular cyclization, elimination reaction, and C?C bond‐cleavage reaction. The two domino reactions have significant advantages including high efficiency, mild reaction conditions, and high tolerance of various functional groups. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(9):2509-2512
A novel cascade reaction has been developed for the synthesis of 2,6‐methanopyrrolo[1,2‐b]isoxazoles based on the gold‐catalyzed generation of an N‐allyloxyazomethine ylide. This reaction involves sequential [3+2]/retro‐[3+2]/[3+2] cycloaddition reactions, thus providing facile access to fused and bridged heterocycles which would be otherwise difficult to prepare using existing synthetic methods. Notably, this reaction allows the efficient construction of three C−C bonds, one C−O bond, one C−N bond and one C−H bond, as well as the cleavage of one C−C bond, one C−O bond and one C−H bond in a single operation. The intermolecular cycloaddition of an N‐allyloxyazomethine ylide and the subsequent application of the product to the synthesis of tropenol is also described. 相似文献
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Tocher DA Drew MG Nag S Pal PK Datta D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(8):2230-2237
HL and MeL are prepared by condensing benzil dihydrazone with 2-formylpyridine and 2-acetylpyridine, respectively, in 1:2 molar proportions. While in a reaction with [Ru(C(6)H(6))Cl(2)]2, HL yields the cation [Ru(C(6)H(6)){5,6-diphenyl-3-(pyridin-2-yl)-1,2,4-triazine}Cl]+, MeL gives the cation [Ru(C(6)H(6))(MeL)Cl]+. Both the cations are isolated as their hexafluorophosphate salts and characterised by X-ray crystallography. In the case of HL, double domino electrocyclic/elimination reactions are found to occur. The electrocyclic reaction occurs in a C=N-N=C-C=N fragment of HL and the elimination reaction involves breaking of a C-H bond of HL. Density functional calculations on model complexes indicate that the identified electrocyclic reaction is thermochemically as well as kinetically feasible for both HL and MeL in the gas phase. For a double domino reaction, similar to that operative in HL, to occur for MeL, breaking of a C-C bond would be required in the elimination step. Our model calculations show the energy barrier for this elimination step to be much higher (329.1 kJ mol(-1)) for MeL than that for HL (96.3 kJ mol(-1)). Thus, the domino reaction takes place for HL and not for MeL. This accounts for the observed stability of [Ru(C(6)H(6))(MeL)Cl]+ under the reaction conditions employed. 相似文献
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《中国化学》2018,36(8):692-697
Cross‐coupling reactions have developed widely and provided a powerful means to synthesize a variety of compounds in each chemical field. The compounds which have C—H bonds are widespread in fossil fuels, chemical raw materials, biologically active molecules, etc. Using these readily‐ available substances as substrates is high atom‐ and step‐economy for cross‐coupling reactions. Over the past decades, our research group focused on finding and developing new strategies for C—H functionalization. Compared with classical C—H activation methods, for example, C—H bonds are deprotonated by strong base or converted into C—M bonds, oxidation‐induced C—H functionalization would be another pathway for C—H bond activation. This perspective shows a brief introduction of our recent works in this oxidation‐induced C—H functionalization. We categorized this approach of these C—H bond activations by the key intermediates, radical cations, radicals and cations. 相似文献