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Transannular chemical reactions are unparalleled in their ability to generate high degrees of stereochemical and architectural complexity in a single transformation. However, the successful application of this approach in synthesis depends on the ability to predict and control the outcome of the transannular reaction. Use of a chiral catalyst in this context represents an attractive, yet unused, strategy. This report describes a catalytic, asymmetric transannnular Diels-Alder (TADA) reaction that affords polycyclic products in high enantiomeric excess. This catalyst system can also alter the inherent diastereoselectivity of cyclizations with substrates containing chiral centers. Additionally, the catalytic enantioselective TADA has been used as the key step in a total synthesis of the sesquiterpene 11,12-diacetoxydrimane; this route may provide a general approach to the polycyclic carbon framework shared by many terpene natural products. 相似文献
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亚胺的催化不对称加成反应是近年来不对称催化反应中的热点研究领域,从手性配体类型的角度总结了近10余年来有机锌试剂在亚胺不对称加成反应中的应用进展. 相似文献
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Enzymes and synthetic chiral catalysts have found widespread application to produce single enantiomers, but in situ switching of the chiral preference of a catalytic system is very difficult to achieve. Here, we report on a light-driven molecular motor with integrated catalytic functions in which the stepwise change in configuration during a 360° unidirectional rotary cycle governs the catalyst performance both with respect to activity and absolute stereocontrol in an asymmetric transformation. During one full rotary cycle, catalysts are formed that provide either racemic (R,S) or preferentially the R or the S enantiomer of the chiral product of a conjugate addition reaction. This catalytic system demonstrates how different molecular tasks can be performed in a sequential manner, with the sequence controlled by the directionality of a rotary cycle. 相似文献
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[目的]探索用微波催化技术快速合成10-乙酰氧基癸酸的工艺。[方法]研制了用微波催化快速合成蜂王酸的中间体10-乙酰氧基癸酸的新工艺：原料为10-羟基癸酸8 g,乙酸酐40 ml;微波功率为400 W,并对产品进行熔点测定、元素分析和红外谱图分析。[结果]微波催化快速合成10-乙酰氧癸酸的新工艺在反应物用量不变的条件下,产率为87.8%,比传统合成工艺增加9.8%,微波合成的每次反应时间由6 h减小为20 min,反应速度是传统合成法的18倍。该产品经过熔点测定、元素分析和红外光谱表征证实为10-乙酰氧基癸酸。[结论]采用微波体加热方式能使反应物快速有效地吸收热能,从而明显加快了反应速度。 相似文献
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对ω－乙酰基莰烯在不同条件下的还原反应进行了研究。结果表明：催化氢化、碲氢化钠还原、钠和氨水还原均具有良好的区位选择性和立体选择性。这些结果为从莰烯合成内型异莰烷基乙酮或内型α－异莰烷基乙醇提供了又一条途径，也为合成外型异莰烷类化合物探索出了一种简便可行的方法。 相似文献
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Seayad A Ahmed M Klein H Jackstell R Gross T Beller M 《Science (New York, N.Y.)》2002,297(5587):1676-1678
The selective synthesis of linear amines from internal olefins or olefin mixtures was achieved through a catalytic one-pot reaction consisting of an initial olefin isomerization followed by hydroformylation and reductive amination. Key to the success is the use of specially designed phosphine ligands in the presence of rhodium catalysts. This reaction constitutes an economically attractive and environmentally favorable synthesis of linear aliphatic amines. 相似文献
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Cirak F Cisternas JE Cuitiño AM Ertl G Holmes P Kevrekidis IG Ortiz M Rotermund HH Schunack M Wolff J 《Science (New York, N.Y.)》2003,300(5627):1932-1936
Because of the small thermal capacity of ultrathin ( approximately 200 nanometers) metal single crystals, it is possible to explore the coupling of catalytic and thermal action at low pressures. We analyzed a chemothermomechanical instability in this regime, in which catalytic reaction kinetics interact with heat transfer and mechanical buckling to create oscillations. These interacting components are separated and explored through experimentation, mathematical modeling, and scientific computation, and an explanation of the phenomenon emerges from their synthesis. 相似文献
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[目的]进行丙酸香叶酯的合成并优化合成条件。[方法]在敞开体系中合成中孔分子筛Al-MCM-41。通过X射线衍射(XRD)、红外光谱(FT-IR)、NH3程序升温脱附(NH3-TPD)、N2吸附-脱附和气相色谱(GC)等方法对所合成样品的结构和催化性能进行表征分析。用其催化合成丙酸香叶酯,考察了反应时间、反应温度、催化剂用量、反应物配比及催化剂再生对香叶醇酯化反应结果的影响。[结果]合成的样品具有中孔分子筛的六方介孔结构以及良好的长程有序性和结晶度,属于典型的中孔材料,分子筛表面有弱酸中心。最佳的反应条件是n(香叶醇)/n(丙酸)=1.0∶1.5,反应温度为120℃,反应时间为8h,但香叶醇的转化率仅为40.01%,丙酸香叶酯的选择性为70.01%。催化剂使用到第5次时有失活现象,可通过焙烧除去掩盖酸中心的积碳,使催化剂的活性和选择性得到恢复。[结论]得到了丙酸香叶酯的合成优化条件,为进一步研究奠定基础。 相似文献
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秸秆燃气合成甲醇的热力学试验研究 总被引：1，自引：1，他引：0
采用热化学方法,将玉米秸秆裂解为生物质燃气,并对该燃气进行优化试验,制备出合成气.在直流流动等温积分反应器中,采用国产C 301铜基催化剂,对玉米秸秆合成气催化合成甲醇进行了试验.运用SHBWR状态方程,计算了加压下秸秆合成气合成甲醇反应体系的密度及状态方程参数. 相似文献
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Hata K Futaba DN Mizuno K Namai T Yumura M Iijima S 《Science (New York, N.Y.)》2004,306(5700):1362-1364
We demonstrate the efficient chemical vapor deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water. Water-stimulated enhanced catalytic activity results in massive growth of superdense and vertically aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above 99.98%. Moreover, patterned, highly organized intrinsic nanotube structures were successfully fabricated. The water-assisted synthesis method addresses many critical problems that currently plague carbon nanotube synthesis. 相似文献
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P G Schultz 《Science (New York, N.Y.)》1988,240(4851):426-433
Chemists and biologists are focusing considerable effort on the development of efficient, highly selective catalysts for the synthesis or modification of complex molecules. Two approaches are described here, the generation of catalytic antibodies and hybrid enzymes, which exploit the binding and catalytic machinery of nature in catalyst design. Characterization of these systems is providing additional insight into the mechanisms of molecular recognition and catalysis which may, in turn, lead to the design of tailor-made catalysts for applications in chemistry, biology, and medicine. 相似文献
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有机相酶催化近年来吸引了众多研究者的关注。本文着重从酶的修饰，酶分子的生物印迹，酶晶体的交联，酶的纯化方式与预处理过程，酶的固定化等脂肪酶的改性因素对酶催化反应的速率与对映体选择性的影响作一综述。 相似文献
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The impact of nanoscience on heterogeneous catalysis 总被引：1，自引：0，他引：1
Bell AT 《Science (New York, N.Y.)》2003,299(5613):1688-1691
Most catalysts consist of nanometer-sized particles dispersed on a high-surface-area support. Advances in characterization methods have led to a molecular-level understanding of the relationships between nanoparticle properties and catalytic performance. Together with novel approaches to nanoparticle synthesis, this knowledge is contributing to the design and development of new catalysts. 相似文献
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The RNA splicing endonuclease cleaves two phosphodiester bonds within folded precursor RNAs during intron removal, producing the functional RNAs required for protein synthesis. Here we describe at a resolution of 2.85 angstroms the structure of a splicing endonuclease from Archaeglobus fulgidus bound with a bulge-helix-bulge RNA containing a noncleaved and a cleaved splice site. The endonuclease dimer cooperatively recognized a flipped-out bulge base and stabilizes sharply bent bulge backbones that are poised for an in-line RNA cleavage reaction. Cooperativity arises because an arginine pair from one catalytic domain sandwiches a nucleobase within the bulge cleaved by the other catalytic domain. 相似文献
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采用超声波辅助的方式制备了新型的酸性双咪唑甲磺酸离子液体,并通过三油酸甘油酯的酯交换反应考查其催化活性及优化实验反应条件,然后将其应用于烤鸭废弃油中以制取生物柴油,对其产物采用气质联用仪(CG-MS)进行了分析。结果表明:在该离子液体作用下,酯交换反应可以在温和的条件下高效地完成,三油酸甘油酯的酯交换产率最高可达95.3%,双咪唑间碳链长短对催化活性影响不明显;催化剂经循环使用6次以后,油酸甲酯产率仍然保持在81%左右。废弃油酯交换制取生物柴油最高产率可达93.9%,且GC-MS检测结果表明生物柴油中脂肪酸甲酯的总含量高达96.9%,其中饱和脂肪酸甲酯含量接近22%,而酯交换未完全的脂肪酸单甘油酯仅0.83%。因此,双咪唑甲磺酸型离子液体能高效催化餐饮废油制备生物柴油。 相似文献