排序方式: 共有202条查询结果,搜索用时 46 毫秒
51.
Anusuya Choudhury Michael Breslav Tong Xiao Kirk L. Sorgi 《Tetrahedron letters》2007,48(17):3069-3072
A one-pot sequential process consisting of nucleophilic substitution of the lithiated acetylides with Weinreb amides followed by a Michael reaction of the extruded N-methoxy-N-methylamine after quenching with saturated NH4Cl, provided β-enamino ketones in high yield and in a single geometrical isomeric form. It has been demonstrated that this method is applicable to a wide variety of such amides and to different acetylides. 相似文献
52.
Lithiation of chloro- and methoxy-(η6-benzene)tricarbonylchromium complexes yielded, after electrophilic quench with a Weinreb amide, the corresponding benzoyl-substituted complexes. One of them has been investigated by an X-ray diffraction study. 相似文献
53.
Surface Modification of Nanometer Silica by N, N''''-dicyclohexyl- carbodiimide Mediated Amidation 总被引:1,自引:0,他引:1
Zhao Xia GUO Jie YU Jian YU* Institute of Polymer Science Engineering Department of Chemical Engineering Tsinghua University Beijing 《中国化学快报》2001,(10)
Nanometer silica has gained ever more attention for its superior properties over conventional micrometer particles and has been widely used as a filler in the manufacture of paints, rubber, plastics and so on1. However it is difficult to get silica mono- dispersed in the matrix due to heavy agglomeration. Surface modification through organic reactions is an efficient way to improve the dispersibility and compatibility with the matrix, thus improving the mechanical properties of the composite… 相似文献
54.
A scalable homogeneous metal‐catalyzed protocol for direct amidation of carboxylic acids is presented. The use of 2–10 mol% of the commercially available Zr(Cp)2(OTf)2·THF results in high yields of amides at moderate temperature, using an operationally convenient reaction protocol that circumvents the use of water scavenging techniques. 相似文献
55.
Man-Yu Wang Hong-Ze Gang Lei Zhou Jin-Feng Liu Bo-Zhong Mu Shi-Zhong Yang 《国际化学动力学杂志》2020,52(2):99-108
The amidation of long-chain fatty acids is the key step for preparing surfactants with excellent interfacial activity. Gas chromatography–mass spectrometry was employed to detect the reactants and products in the direct amidation reactions. The conversion and the concentration of the amides in the reaction process were also investigated to determine the best catalyst, the reaction rate constants, and activation energy. It was identified that the amidation reaction of the long-chain phenyl fatty acid was a zero-order reaction and 3,4,5-trifluorophenylboronic acid was the most effective catalyst by which the activation energy reduced to 55.79 kJ/mol from 95.44 kJ/mol. The method can be applied to other long-chain fatty acids, saturated or unsatureated. The turning-over-temperature was 156°C, over which high yields can be achieved without any catalyst. These provide a reference for the preparation of long-chain fatty acid amides. 相似文献
56.
Maxime Gauthier Dr. Frédéric Coutrot 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(70):17576-17580
This paper reports the synthesis and study of new pH-sensitive DB24C8-based [2]rotaxane molecular shuttles that contain within their axle four potential sites of interaction for the DB24C8: ammonium, amine, Weinreb amide, and ketone. In the protonated state, the DB24C8 lay around the best ammonium site. After either deprotonation or deprotonation-then-carbamoylation of the ammonium, different localizations of the DB24C8 were seen, depending on both the number and nature of the secondary stations and steric restriction. Unexpectedly, the results indicated that the Weinreb amide was not a proper secondary molecular station for the DB24C8. Nevertheless, through its methoxy side chain, it slowed down the shuttling of the macrocycle along the threaded axle, thereby partitioning the [2]rotaxane into two translational isomers on the NMR timescale. The ketone was successfully used as a secondary molecular station, and its weak affinity for the DB24C8 was similar to that of a secondary amine. 相似文献
57.
J. Meuldijk B.H.P. van de Kruijs J.A.J.M. van Vekemans L.A. Hulshof R. Duchateau C.E. Koning 《Macromolecular Symposia》2011,302(1):69-79
Summary: Microwave irradiation was used for the amidation of a nitrile with an amine with a freshly prepared zirconium-based heterogeneous catalyst. Microwave irradiation selectively heats the catalyst which enhances its activity as compared to conventional heating. The difference between microwave heating and conventional heating disappears when Zr(OH)4 is used instead of ZrO2, indicating a microwave-induced shift in the hydrolysis equilibrium, i.e. the distribution of ZrO2, ZrO(OH)2 and Zr(OH)4, of the zirconium-based catalyst. The catalyst efficiently catalyzes the amidation of valeronitrile with n-hexylamine with conventional as well as with microwave heating. Zr(OH)4 was also used for the polymerization of 6-aminocapronitrile using conventional and microwave heating. With both heating methods a relatively low molecular weight polymer with a Mn of 4000 g/mol was obtained in a sealed vessel, due to the presence of water and ammonia. A post-polymerization step under microwave irradiation, with active removal of water and ammonia shifts Mn to 10000 g/mol. Pressure decrease to facilitate water removal resulted in products with higher molecular weights. A pressure reduction to 50 Pa and operation in an argon atmosphere at 230 °C resulted in nylon-6 with a Mn of 65000 in rather short reaction times. Lower pressures led to end-biting and evaporation of the volatile ε-caprolactam at 230 °C. As a consequence the resulting product has than a much lower molecular weight. The combination of a heterogeneous zirconium based catalyst and microwave heating is promising for process intensification for nylon-6 production. 相似文献
58.
Loreto Legerén 《Tetrahedron letters》2010,51(31):4053-5080
Alkylation of l-prolinamide with 3-(chloromethyl)-2-halopyridines, followed by cyclization through an intramolecular Pd-catalysed amidation, provided an entry to the pyrido[2,3-e]pyrrolo[1,2-a][1,4]diazepin-10-one scaffold. Furthermore, a synthetic route towards diverse new pyrido[f]pyrrolo[1,2-a][1,4]diazepin-7-ones has been developed by acylation of contiguously substituted (aminomethyl)halopyridines with Boc-l-proline followed by intramolecular amination. 相似文献
59.
The synthesis of racemic anatoxin a ( 1a ) from cycloocta‐1,5‐diene via its 1 : 1 cycloadduct with N‐chlorosulfonyl isocyanate is described. The N‐unsubstituted β‐lactam 2b was converted to a β‐amino ester 3 which was then submitted to a Pd‐catalyzed cyclization to afford the conjugated ester 4a . The N‐tosyl derivative 4b was then elaborated into N‐tosylanatoxin a ( 1b ) via a Weinreb amide. 相似文献
60.
Lipase-catalyzed amidation of 2-[2-(ethoxycarbonyl)ethyl]-1,1′-binaphthyl [(±)-3] yielded optically active (S)-3 and 2-[2-(2-cyanoethylaminocarbonyl)ethyl]-1,1′-binaphthyl [(R)-6a] with high enantiomeric excess. For these lipase-catalyzed amidations, the optimal alkyl chain length between the binaphthyl ring and the ester group was determined to be an ethylene spacer. 相似文献