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排序方式: 共有125条查询结果,搜索用时 15 毫秒
31.
Yu-Huan Geng Dr. Yuan-Zhao Hua Dr. Shi-Kun Jia Prof. Dr. Min-Can Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(16):5130-5135
The first regio-, diastereo-, and enantioselective direct Mannich reaction of β,γ,-unsaturated ketones with benzoxazinone cyclic imines was enabled by Lewis acid/Brønsted base cooperative catalysis. The dinuclear zinc complex catalyzed the reaction of a broad range of β,γ-unsaturated ketones to proceed at the α-site exclusively, leading to corresponding adducts with two consecutive tertiary carbon stereocenters in diastereomeric ratios of up to >20:1 and enantioselectivities generally in the 90–99 % ee range. These products were used as general intermediates in the synthesis of multisubstituted cyclocanalines, tetrahydro pyridazinones, and 4H-furo[2,3-b][1,4]benzoxazine derivatives. 相似文献
32.
33.
Virgil Percec Cristian Grigoras Hyoung-J. Kim 《Journal of polymer science. Part A, Polymer chemistry》2004,42(3):505-513
TERMINI stands for irreversible terminator multifunctional initiator and represents a new concept elaborated in our laboratory for the design of novel macromolecules with complex architecture from a diversity of commercial monomers. TERMINI is a masked multifunctional initiator that quantitatively interrupts a living polymerization. After demasking, the TERMINI-derived repeat unit provides access to a quantitative reinitiation of the same living polymerization in more than one direction, thus becoming a branching point. In this article, with a combination of self-regulated metal-catalyzed living radical polymerization and TERMINI, we demonstrate a new method for the divergent synthesis of dendritic poly(methyl methacrylate) containing a bifunctional core at its focal point. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 505–513, 2004 相似文献
34.
利用排序原理证明了数列{(1 1/n)~n}收敛性,级数∑(n!e~n)/(n~n p)在p≤3/2时是发散的和几个不等式。 相似文献
35.
Hui-Yun Luo Jia-Wei Dong Yu-Yang Xie Xu-Feng Song Deng Zhu Tongmei Ding Prof. Dr. Yuanyuan Liu Prof. Dr. Zhi-Min Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(67):15411-15418
A divergent strategy for the facile preparation of various enantioenriched phenylthio-substituted lactones was developed based on Lewis base/Brønsted acid co-catalyzed thiolation of homoallylic acids. The acid-controlled regiodivergent cyclization (6-endo vs. 5-exo) and acid-mediated stereoselective rearrangement of phenylthio-substituted lactones were explored. Experimental and computational studies were performed to clarify the origins of the regioselectivity and enantioselectivity. The calculation results suggest that C−O and C−S bond formation might occur simultaneously, without formation of a commonly supposed catalyst-coordinated thiiranium ion intermediate and the potential π–π stacking between substrate and SPh as an important factor in the enantio-determining step. Finally, this methodology was applied in the rapid syntheses of the bioactive natural products (+)-ricciocarpin A and (R)-dodecan-4-olide. 相似文献
36.
Robert J. MacG. Dawson 《Geometriae Dedicata》2000,80(1-3):297-309
A generalized face number, typically taking negative rational values for a regular hyperbolic honeycomb, is constructed in three different ways – via differential geometry, combinatorics, and divergent series. 相似文献
37.
ZhiJunYU QiZhenZHANG QiFengZHOU 《中国化学快报》2003,14(5):465-467
The preparation of carbosilane dendrimers with cores of myo-inositol and the outmost periphery grougs of allyl groups has been reported.By using alternate hydrosilylation and alkenyiation reactions,the dendrimer have been carried up to the third generation with 48 allyl groups on the periphery. 相似文献
38.
Koji Takagi Tatsuya Hattori Hideo Kunisada Yasuo Yuki 《Journal of polymer science. Part A, Polymer chemistry》2000,38(24):4385-4395
Two types of dendrimers with a 1,3,5‐triazine ring at the branch point were synthesized by divergent and convergent methods. The divergent method began with 2,4,6‐tris(p‐nitroanilino)‐1,3,5‐triazine as a trifunctional core. Each cycle involved the reduction of the peripheral NO2 group followed by a reaction with 2‐chloro‐4,6‐bis(p‐nitroanilino)‐1,3,5‐triazine. The synthetic cycle was completed by the coupling with 2,4‐dianilino‐6‐chloro‐1,3,5‐triazine (DACT) to eventually accomplish second‐generation dendrimers ([G2]3‐C) bearing 12 benzene rings at their edge. The convergent approach started with the reaction of DACT with p‐nitrophenol to give rise to 2,4‐dianilino‐6‐(p‐nitrophenoxy)‐1,3,5‐triazine. The synthetic cycle consisted of reduction of the NO2 group and coupling with 2,4‐dichloro‐6‐(p‐nitrophenoxy)‐1,3,5‐triazine. The final step was the connection of each monodendron with cyanuric chloride to produce tridendron; in this way, the second‐generation dendrimer ([EG2]3‐C) was obtained. Gel permeation chromatography analyses indicated the aggregation of dendrimers in solution. Ultraviolet spectroscopic analyses revealed that the larger dendrimer had a more conjugated electron system from the core to the periphery. The thermal properties were evaluated by thermogravimetric analysis (TGA); excellent heat resistance was indicated, especially in [G1]3‐C, which included alternately imine‐like nitrogen‐linked 1,3,5‐triazine and benzene rings. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4385–4395, 2000 相似文献
39.
激光窗口热效应对光束发散角的影响 总被引:6,自引:4,他引:2
以DF激光器CaF_2输出窗口为例计算了三种输出功率(10~3W,10~4W,10~5W)情况下,窗口材料的温升、波阵面畸变及对光束发散角的影响。计算中窗口直径为40mm,厚度为10mm,光束直径为20mm。 相似文献
40.
中心为氨基、末端为硝基的苯乙炔树枝状分子的合成 总被引:1,自引:0,他引:1
将固定相合成与“收敛/发散”方法相结合,合成了第一、二代苯乙炔树枝状分子.通过Heck-Cassar-Sonogashira-Hagihara偶联反应,将其中心和末端分别修饰上供电子的氨基和拉电子的硝基,得到第一、二代中心为氨基、末端为硝基的苯乙炔树枝状分子NH2-G1-(NO2)2和NH2-G2-(NO2)4.用傅里叶变换红外光谱跟踪了整个固定相合成过程.苯乙炔树枝状分子的紫外-可见吸收光谱呈现出规律性变化. 相似文献