共查询到20条相似文献,搜索用时 203 毫秒
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《有机化学》2014,(7)
正手性2H-吡咯类化合物是有机合成中一类重要的合成中间体.通过催化不对称去芳构化反应,可以实现直接由吡咯类化合物来构建这类骨架.然而,目前文献上报道的对取代吡咯类化合物的直接催化去芳构化反应主要集中在过渡金属催化的不对称[4+3]环加成反应和氢化反应.由于反应过程中可能面临的化学选择性、区域选择性和对映选择性等挑战性问题,通过烷基化反应来实现吡咯环的分子间不对称去芳构化反应迄今还没有被报道.中国科学院上海有机化学研究所游书力课题组成功地通过使用烯丙基取代反应实现了取代吡咯的分子间催化不对称去芳构化.使用取代的吡咯化合物1和烯丙基碳酸酯2在金属钯和商业可得的手性配体(R)-segphos的作用下,可以以高达 相似文献
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十二顶点碳硼烷是一类含有碳、氢及硼原子的簇合物,具有特殊的热稳定性和化学稳定性,在医药、材料、能源、配位化学及金属有机化学中都得到广泛的应用.近年来,过渡金属催化的碳硼烷直接硼-氢键活化发展迅速,为硼顶点选择性官能团化提供了一系列新的高效路径.总结了利用过渡金属催化硼-氢键活化策略来实现邻碳硼烷硼-硼、硼-氮、硼-氧、硼-硫及硼-卤键构建的研究进展,同时对部分反应机理进行了讨论,并就该研究领域所面临的挑战和发展前景进行了展望. 相似文献
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Brigitte Voit Sven Fleischmann Hartmut Komber Arnulf Scheel Katrin Stumpe 《Macromolecular Symposia》2007,254(1):16-24
Summery: The potential of cycloaddition (CA) reactions for the synthesis of dendritic polymers is pointed out. The [4 + 2] Diels Alder cycloaddition as well as 1,3-dipolar CA reactions including “click chemistry” are addressed, and the advantages of these reactions like high selectivity, thus high tolerance towards additional functionalities, high yields and synthesis under mild reaction conditions are highlighted. New perfectly branched dendrimers as well as hyperbranched polymers have been prepared and modified using the 1,3-dipolar cycloaddition reaction of azines with alkynes. The 1,3-dipolar CA reaction of bisazine with maleimides results in hyperbranched and thus, irregular and broadly distributed polymers though with a degree of branching of 100% due to special intermediate formation. The [4 + 2] Diels Alder cycloaddition was successfully applied for the synthesis of highly branched polyphenylene structures using the AB2 + AB and the A2 + B3 approach. CA reactions are also very suitable for highly efficient polymer analogous reactions and thus, they can also be used to prepare complex polymer architectures like dendronized polymers. 相似文献
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过渡金属催化环加成反应是合成单环及多环化合物的重要方法,也是有机化学的研究热点之一.综述了近年来铱催化环加成反应的研究进展,主要包括了[2+2+1],[2+2+2],[4+2],1,3-偶极环加成反应等,及少量关于[3+2+2],[3+2],[5+1]环加成反应的报道,并讨论了部分铱催化环加成反应机理. 相似文献
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Three-component cycloadditions: the first transition metal-catalyzed [5+2+1] cycloaddition reactions
Wender PA Gamber GG Hubbard RD Zhang L 《Journal of the American Chemical Society》2002,124(12):2876-2877
Prompted by our studies of transition metal-catalyzed [4+4], [4+2], [5+2], and [6+2] cycloadditions and by the view that these two-component reactions could be intercepted by a third component of one or more atoms, a new three-component transition metal-catalyzed cycloaddition is described. This new [5+2+1] cycloaddition proceeds in good to excellent yield and with high or complete regioselectivity with a variety of carbonyl-substituted alkynes to give bicyclo[3.3.0]octenone adducts, resulting from transannular closure of the intermediate eight-membered-ring cycloadduct. Effects of concentration, temperature, pressure, and catalyst loading on the efficiency of the reaction are discussed. This process provides access to complex building blocks for synthesis based on simple, readily available components. 相似文献
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Cycloaddition reactions compose one of the most important classes of reactions when it comes to the simultaneous formation of several bonds in one reaction step. The de novo construction of carbocyclic aromatic systems from acetylenes was also found as an excellent possibility for the assembly of heteroaromatic systems. The transition metal-catalysed [2 + 2 + 2] cycloaddition reaction constitutes a fascinating tool for the synthesis of pyridines from nitriles and the most recent developments demonstrate the ability to control the substitution pattern as well as the possibility of introducing chirality by the use of achiral substrates and a chiral catalyst under mild conditions. In this tutorial review we are focusing on the de novo construction of pyridine ring systems by the transition metal-catalysed [2 + 2 + 2] cycloaddition reaction. After surveying the mechanistic features and intermediates of the reaction depending on the different metal complexes used, we depict the preparation of achiral pyridine derivatives. The last section describes the advances in the synthesis of chiral pyridines and biaryls using the cyclotrimerization method. The various possibilities of introducing chirality by catalytic means are presented and illustrated by instructive examples. This review will be of interest for people active in: Organic Chemistry, Organometallic Chemistry, Transition Metal Chemistry, Stereoselective Synthesis, Heterocyclic Chemistry. 相似文献
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Kukhtin-Ramirez反应是有机化学中一类重要的极性反转反应.利用三价磷的还原性对α-羰基酮化合物进行极性反转,所生成的Kukhtin-Ramirez活性中间体在诸多转化中都展现出了其作为1,1-偶极子的化学性质.近年来关于该活性中间体的反应研究主要包括:极性X—H键插入反应、还原性加成反应、形式[2+1]环加成反应、形式[4+1]环加成反应、形式[4+2]环加成反应.这些转化为一些重要的多官能团化合成中间体及结构复杂的环状化合物提供了高效简洁的合成方法,凸显了Kukhtin-Ramirez极性反转反应在有机合成中的重要性. 相似文献
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Amino acid-based catalysts have been intensively researched in recent years. Amino acid-derived phosphines possess high nucleophilicity and exhibit unique catalytic activities in asymmetric synthesis. L-Threonine and valine are most utilized natural amino acids in the preparation of chiral phosphines. The efficient and versatile chiral phosphine catalysts are applied in a wide range of reactions such as MBH reaction, Rauhut–Currier reaction, Michael addition, [4 + 2]-annulation, [3 + 2]-annulation, 1,4-dipolar cycloaddition. They are also widely used in the construction of core structures of natural products. Amino acid-based phosphine catalysts and their applications in asymmetric synthesis are summarized. 相似文献
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Although azaoxyallyl cations are widely used as 1,3‐dipoles for various cycloaddition reactions leading to nitrogen‐containing heterocycles, their application in higher‐order cycloaddition reaction remains scarce. Herein, we present the [8+3]‐cycloaddition reaction of tropones with in situ generated azaoxyallyl cations allowing the one‐step construction of cycloheptatriene‐fused 1,4‐oxazinones in moderate to good yields. This base‐promoted new carbon‐oxygen and carbon‐nitrogen bond‐forming reaction takes place under mild conditions in the absence of transition metal catalysts. 相似文献
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Ahmad Shaabani Heshmatollah Sepahvand Mostafa M. Amini Alireza Hashemzadeh Mahmoud Borjian Boroujeni Elham Badali 《Tetrahedron》2018,74(15):1832-1837
The tandem oxidative three-component synthesis of two types of the heterocycles such as furans and imidazopyridines, via isocyanides [1+4] cycloaddition reactions in the presence of MIL-101(Cr) under aerobic conditions are reported. When the 4-toluenesulfonylmethyl isocyanide was used, an unexpected [3+2] cycloaddition reaction of isocyanides with aldehydes accomplished and dihydrophenyloxazoles and phenyloxazoles produced. These syntheses were successfully carried out using a wide scope of the substrates. 相似文献
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[reaction: see text] Ab initio and density functional studies (DFT) on cycloaddition reactions of 1,3-diazabuta-1,3-dienes with ketenes are reported. The vinylic (C=C) and the carbonyl (C=O) units of the ketenes are found to participate in concerted asynchronous [4 + 2] cycloaddition reactions. The transition states (3t, 4t, and 7t) for these paths have been located on the PE surface at the correlated levels of ab initio calculations. A reasonable mechanism for the formation of [4 + 2] and [2 + 2] adducts is presented. 相似文献
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Anna E. Hurtley Dr. Zhan Lu Prof. Tehshik P. Yoon 《Angewandte Chemie (International ed. in English)》2014,53(34):8991-8994
[2+2] Photocycloadditions of 1,3‐dienes represent a powerful yet synthetically underutilized class of reactions. We report that visible light absorbing transition metal complexes enable the [2+2] cycloaddition of a diverse range of 1,3‐dienes. The ability to use long‐wavelength visible light is attractive because these reaction conditions tolerate the presence of sensitive functional groups that might be readily decomposed by the high‐energy UVC radiation required for direct photoexcitation of 1,3‐dienes. The resulting vinylcyclobutane products are poised for a variety of further diversification reactions, and this method is consequently expected to be powerfully enabling in the synthesis of complex organic targets. 相似文献