共查询到20条相似文献,搜索用时 113 毫秒
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羧酸具有价廉、易得、易于运输存储等特点。与传统的有机金属试剂相比,羧酸经过渡金属催化脱羧后生成的有机金属中间体同样具有很好的与亲核试剂偶联或与亲电试剂反应的活性,以羧酸为反应试剂经脱羧与碳原子或杂原子偶联为化学键的构建提供了新的思路,尤为重要的是羧酸经脱羧偶联通常只产生一分子二氧化碳。大量的脱羧碳-碳、碳-杂键成键反应已被报道,其中包括SP碳羧酸、SP2碳羧酸、SP3碳羧酸。本文着重介绍羧酸脱羧与杂原子偶联反应,包括脱羧质子化、碳-氮、碳-氧、碳-硫、碳-硒、碳-卤、碳-磷键成键反应。 相似文献
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设施土壤长期在“高温、高湿、高度连作、连续过量施肥、无降水淋洗”等特殊环境条件下,有机碳、磷明显富集,容易发生连作障碍,并且会影响地下水的质量。分析土壤中有效磷含量对有机碳组分的影响,对于调控土壤肥力水平、维持农业的可持续发展、改善生态环境均具有重要的意义。以北京地区典型设施菜地为研究对象,研究不同有效磷含量对土壤有机碳组分的影响,结果发现:土壤总有机碳含量与有效磷含量呈正相关,其中相关性最强的组分是活性有机碳以及胡敏酸等惰性有机碳;土壤微生物量碳在Olsen-P 60 mg/kg条件下随着磷含量的增加急剧增加,当超过该含量时变化缓慢而逐渐趋于稳定。 相似文献
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1前言近两年来,在C60衍生物的合成中,一些有机活性中间体扮演了极为重要的角色。笔者通过有机叠氯化物热解生成的Nitrene中间体。合成了一系列氛杂C60衍生物[1,2]。Wudl和Tsuda等人[3.4]用Carbene活性中间体也会成了一些C60衍生物。笔者认为,虽然C60与本相比,具有较小的芳香性,但其化学反应活性仍然不是很强,所以一些活性中间体与C60反应为合成各种C60衍生物提供了一个很好的途径。活性中间体Carbene,Nitrone的深入研究十分必要。木文拟对这些中间体的羊城态和三线态及发光现象作以探讨。2结构特性2.1单线态单线态卡宾常写作1… 相似文献
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Summary A new route for the preparation of soluble fullerenated polymer through the reaction of carbanion intermediates of polymers with fullerenes, particularly C60, is demonstrated. Confirmation of the covalent attachment of C60 to the polystyrene backbone is by a variety of techniques such as UV-Vis, FT-IR, TGA, SEM and 13C NMR etc. The product, which has a visibly brownish yellow cast when compared with the unreacted polymer, is soluble in some common organic solvents. The thermal stability of pure polystyrene is enhanced by C60-chemical modification, and no bonds within the carbon sphere are broken. 相似文献
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Electrochemically induced cyclization of bromoamides to β-lactams has been achieved in room-temperature ionic liquids (RTILs). The use of volatile, organic solvents (VOCs) and of supporting electrolytes may be avoided. Proton exchange reaction between amide substrates and suitable electrogenerated bases gives rise to a C4 carbanion which undergoes cyclization to β-lactam via intramolecular nucleophilic substitution (C3-C4 bond formation). β-Lactams have been isolated in good to elevated yields. The “non innocent” nature of the RTILs (imidazolium-based salts) is considered. Proton exchange reaction between N-dialkylimidazolium cation and EGB yielding N-heterocyclic carbene is discussed. 相似文献
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Vinylic tellurides are of importance due to their useful behavior as synthons and intermediates. Recently, the use of these compounds in place of vinylic halides or triflates in the palladium-catalyzed cross-coupling reaction has emerged as a powerful tool in the preparation of conjugated enyne and enediyne. In this way, vinylic tellurides can behave as aryl or vinyl carbocation equivalents. This review focuses on methods that involve the use of vinylic tellurides in palladium-catalyzed cross coupling reaction. 相似文献
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Benzaldehyde lyase from the Pseudomonas fluorescens catalyzes the reaction of aromatic aldehydes with nitroso compounds and furnishes N‐arylhydroxamic acids in high yields. Aromatic aldehydes and benzoins are converted into enamine‐carbanion‐like intermediates prior to their reaction with nitroso compounds. The kinetic resolution of rac‐2‐hydroxy‐1,2‐diphenylethanones furnished (S)‐benzoins and arylhydroxamic acids with high enantioselectivities and conversions. 相似文献
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环己基苯经过氧化反应可生产苯酚和环己酮,还可以用作锂离子电池电解液的添加剂,也可用作柴油的十六烷值调和组分,是一种高附加值、有市场潜力的精细化学品。本文介绍了国内外通过苯与环己烯烷基化合成环己基苯及所用催化剂的研究进展,总结了苯加氢烷基化反应机理和反应路径的研究成果,包括加氢烷基化活性的来源、中间产物和碳正离子中间体的推断以及各反应产物的形成。通过对加氢烷基化机理的认识,回顾了加氢烷基化催化剂的设计思路和发展历程。最后指出可开发用于苯与环己烯烷基化的B酸型、B-L酸型以及固载化离子液体等新型催化剂。提出可借助最新的碳正离子研究手段对加氢烷基化机理进行补充完善,并认为可利用多级孔沸石作为加氢烷基化催化剂的酸性载体。 相似文献
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Dr. Nicole G. H. Leferink Dr. Andrés M. Escorcia Bodi R. Ouwersloot Dr. Linus O. Johanissen Prof. Dr. Sam Hay Dr. Marc W. van der Kamp Prof. Dr. Nigel S. Scrutton 《Chembiochem : a European journal of chemical biology》2022,23(5):e202100688
Monoterpene synthases are often promiscuous enzymes, yielding product mixtures rather than pure compounds due to the nature of the branched reaction mechanism involving reactive carbocations. Two previously identified bacterial monoterpene synthases, a linalool synthase (bLinS) and a cineole synthase (bCinS), produce nearly pure linalool and cineole from geranyl diphosphate, respectively. We used a combined experimental and computational approach to identify critical residues involved in bacterial monoterpenoid synthesis. Phe77 is essential for bCinS activity, guiding the linear carbocation intermediate towards the formation of the cyclic α-terpinyl intermediate; removal of the aromatic ring results in variants that produce acyclic products only. Computational chemistry confirmed the importance of Phe77 in carbocation stabilisation. Phe74, Phe78 and Phe179 are involved in maintaining the active site shape in bCinS without a specific role for the aromatic ring. Phe295 in bLinS, and the equivalent Ala301 in bCinS, are essential for linalool and cineole formation, respectively. Where Phe295 places steric constraints on the carbocation intermediates, Ala301 is essential for bCinS initial cyclisation and activity. Our multidisciplinary approach gives unique insights into how carefully placed amino acid residues in the active site can direct carbocations down specific paths, by placing steric constraints or offering stabilisation via cation-π interactions. 相似文献