共查询到20条相似文献,搜索用时 31 毫秒
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LU TaJung 《高等学校化学研究》2001,17(3)
The use of microwave technology in accelerating organic reactions has received intense attention leading to immense growth recently. Accordingly, we have been interested in improving the efficacy of organic processes by microwave irradiation. Here we report our results on the microwave assisted 1,3-dipolar cycloaddition reaction of nitrile oxides with allylic alcohols, the cleavage reaction of 1,3-diketones under alkaline conditions, and the formation of carbamates from isocyanates with alcohols. The reactions carried out under microwave irradiation, in general, required considerably less reaction time and afforded the desired products in higher yields than those under classical conditions. In all the cases we have studied, the procedures are simplified, the purity of the products are higher, and the cost of reaction is greatly reduced employing microwave. 相似文献
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脯氨酸催化的不对称有机反应 总被引:1,自引:0,他引:1
脯氨酸作为一种结构简单、商品化的、廉价小分子手性催化剂,在多种不对称催化反应中表现出非常好的催化性能,本文综述了近年来脯氨酸直接催化的不对称有机反应涉及Aldol反应,Mannich反应,Michael反应,Diels-Alder反应,直接α-胺化反应,α-氧胺化反应,Baylis-Hillman反应,还原反应和氧化反应的进展并展望了其应用前景。 相似文献
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有机小分子催化的不对称合成反应是目前研究最为活跃的领域之一. 不对称Strecker反应是合成光学活性α-氨基酸衍生物的有效手段. 目前报道的催化不对称Strecker反应的有机催化剂主要有手性胍类、手性(硫)脲衍生物、氮-氧偶极化合物、手性Brønsted酸等, 取得了良好的催化活性和对映选择性. 对各类有机小分子催化剂在有机催化不对称Strecker反应中的应用研究进展, 以及催化剂结构与反应条件对催化活性和不对称诱导作用的影响进行了简要评述. 相似文献
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Dr. Chun-Wei Chang Mei-Huei Lin Dr. Cheng-Chung Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(8):2556-2568
Chemical synthesis is one of the practical approaches to access carbohydrate-based natural products and their derivatives with high quality and in a large quantity. However, stereoselectivity during the glycosylation reaction is the main challenge because the reaction can generate both α- and β-glycosides. The main focus of the present article is the concept of recent mechanistic studies that have applied statistical analysis and quantitation for defining stereoselective changes during the reaction process. Based on experimental evidence, a detailed discussion associated with the mechanism and degree of influence affecting the stereoselective outcome of glycosylation is included. 相似文献
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"水上"有机反应的发展是水相绿色合成反应研究领域中的一个突破。体系的非均相性质是"水上"反应的基本特征。水不仅是重要的绿色反应介质,在大多数"水上"有机反应中都能观察到水对反应的速度和选择性有明显的提升作用。采用"水上"反应的条件,可以使反应的规模扩大,有利于产物的分离、纯化。本文以反应的类型分类综述了近年来有关"水上"有机反应研究的进展,以及在绿色有机合成中的应用。 相似文献
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Claire Empel Sripati Jana Tim Langletz Prof. Dr. Rene M. Koenigs 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(12):e202104321
In this combined computational and experimental study, the C−H functionalization of 2-phenyl pyridine with diazoalkanes was investigated. Initial evaluation by computational methods allowed the evaluation of different metal catalysts and diazoalkanes and their compatibility in this C−H functionalization reaction. With these findings, suitable reaction conditions for the C−H methylation reactions were quickly identified by using highly reactive TMS diazomethane and C−H alkylation reactions with donor/acceptor diazoalkanes, which is applied to a broad scope on alkylation reactions of 2-aryl pyridines with TMS diazomethane and donor/acceptor diazoalkane (51 examples, up to 98 % yield). 相似文献
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Takahito Kasahara Young Jin Jang Léanne Racicot Dimitrios Panagopoulos Dr. Steven H. Liang Prof. Dr. Marco A. Ciufolini 《Angewandte Chemie (International ed. in English)》2014,53(36):9637-9639
A metathesis reaction occurs when a diaryliodonium triflate is heated with an aryl iodide, resulting in the formation of a new diaryliodonium triflate. 相似文献
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Cyril A. Grob 《Angewandte Chemie (International ed. in English)》1976,15(10):569-575
Attempts to gauge the effect of polar substituents on organic reaction rates by means of “inductive substituent constants” are based on the assumption that these effects are independent of the type of reaction observed. The measured rate constants of nucleophilic substitution reactions show, however, that this assumption is only partly justified even for saturated molecules. It is invalid if the substituent and the reaction center are an electron donor and an electron acceptor, respectively, which are hyperconjugated by way of σ-bonds. In extreme cases the resulting polarization can lead to heterolytic fragmentation. 相似文献
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Takahito Kasahara Young Jin Jang Lanne Racicot Dimitrios Panagopoulos Steven H. Liang Marco A. Ciufolini 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(36):9791-9793
A metathesis reaction occurs when a diaryliodonium triflate is heated with an aryl iodide, resulting in the formation of a new diaryliodonium triflate. 相似文献
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Heck reaction is one of the most important carbon-carbon bond forming reactions with wide applications in organic synthesis.Considerable advances of enantiosele... 相似文献
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Dr. Pascal Vermeeren Dr. Trevor A. Hamlin Prof. Dr. F. Matthias Bickelhaupt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(40):e202200987
The catalytic effect of ionization on the Diels-Alder reaction between 1,3-butadiene and acrylaldehyde has been studied using relativistic density functional theory (DFT). Removal of an electron from the dienophile, acrylaldehyde, significantly accelerates the Diels-Alder reaction and shifts the reaction mechanism from concerted asynchronous for the neutral Diels-Alder reaction to stepwise for the radical-cation Diels-Alder reaction. Our detailed activation strain and Kohn-Sham molecular orbital analyses reveal how ionization of the dienophile enhances the Diels-Alder reactivity via two mechanisms: (i) by amplifying the asymmetry in the dienophile's occupied π-orbitals to such an extent that the reaction goes from concerted asynchronous to stepwise and thus with substantially less steric (Pauli) repulsion per reaction step; (ii) by enhancing the stabilizing orbital interactions that result from the ability of the singly occupied molecular orbital of the radical-cation dienophile to engage in an additional three-electron bonding interaction with the highest occupied molecular orbital of the diene. 相似文献
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The reaction of two amidoximes 4 with ethyl orthoacetate in the presence of an acid catalyst gave triazine N-oxides 7 . A mechanism via a Beckmann rearrangement to a carbodiimide, followed by reaction with amidoxime and the ortho ester, is proposed. 相似文献
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Glycosylations are notoriously difficult reactions that require extensive optimization regarding the type of anomeric leaving group, solvent, reaction temperature, and reaction time. Described is the use of a silicon‐based microreactor to screen reaction conditions and to scale‐up synthetic procedures. For the first time, glycosyl phosphates were employed in a microreactor. The optimized reaction conditions were successfully transferred to a batch process. 相似文献
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1-Chloro-1-(2′,3′,5′,6′-tetrafluoropyridyl)tetrafluoroethane, obtained by reaction of chlorotrifluoroethylene with pentafluoropyridine in the presence of caesium fluoride, was dehalogenated over iron at 310°, giving perfluoro-4-vinylpyridine (IV). Reactions of (IV) have been surveyed; nucleophilic attack occurs at both the ring and the difluoromethylene group using MeO- but with PhO-, selective attack at the difluoromethylene group occurred. A dimer is produced by reaction of (IV) with CsF and the intermediate carbanion was trapped with tetrafluoropyridazine. Thermal cyclodimerisation of (IV) gave a single isomer whose structure was established by n.m.r. and by defluorination to a cyclobutene. Cyclobutanes were formed in thermal cycloaddition reactions with chlorotrifluoroethylene and with hexafluoropropene. Photochemical reaction of (IV) with hexafluoroacetone gave an oxetane. 相似文献
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Anatoli L. Poznyak Valeri I. Pavlovski 《Angewandte Chemie (International ed. in English)》1988,27(6):789-796
Three types of photochemical reaction of coordination compounds are well-known and have often been discussed: redox reactions, substitutions, and isomerizations. Less well known is a fourth type of reaction, which occurs fairly frequently: reaction of the ligands themselves. It is the purpose of this article to fill the corresponding gap in the photochemical literature and to summarize our current knowledge of such reactions and of their mechanisms and possible applications. 相似文献
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The effects of hetero atoms within the substrate molecule and the number of available hydrogen atoms in the hydrogen abstraction reaction are considered. Chlorodifluoromethyl radicals are generated by the photolysis of 1,3-dichlorotetrafluoroacetone and the substrate molecules used are dimethyl ether, trimethylamine and tetramethylsilane. The Arrhenius parameters for the hydrogen abstraction reaction have been calculated and compared with those obtained using other radicals. The role of secondary radical decomposition is considered. 相似文献