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171.
Organocatalysis mediated by (thio)urea derivatives 总被引:1,自引:0,他引:1
Connon SJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(21):5418-5427
Over the last decade the potential for N,N-dialkyl(thio)urea derivatives to serve as active metal-free organocatalysts for a wide range of synthetically useful reactions susceptible to the influence of general acid catalysis has begun to be realised. This article charts the development of these catalysts (with emphasis on the design principles involved), from early "proof-of-concept" materials to contemporary active chiral (bifunctional) promoters of highly selective asymmetric transformations. 相似文献
172.
Guo Xiaoguang Shang Jianpeng Li Jian Wang Liguo Ma Yubo Shi Feng Deng Youquan 《中国化学》2010,28(2):164-170
A series of silica gel immobilized lanthanum catalysts were prepared for the atom‐economy synthesis of N‐substituted carbamates from urea derivatives and dimethyl carbonate. The La/SiO2 catalysts with lanthanum loadings varied from 1.3 wt% to 8.5 wt% were characterized by AES, BET, XRD, TEM, FT‐IR, XPS and TPD. According to the characterization, lanthanum species with particle sizes of 5–10 nm on the surface of silica gel were formed. The catalysts were all amorphous and the surface areas were 336.5–530.2 m2/g. NH3‐TPD analysis showed that all samples exhibited similar acid strength with different acid amounts. FT‐IR measurement indicated that the component of lanthanum species on the catalyst surface were La(OH)3, LaOOH and hydrated La2O3. Also, the peak value of the absolute amount of LaOOH was obtained with 4.3 wt% lanthanum loading. The BET surface area decreased dramatically when the lanthanum loading was above 4.3 wt%. In consideration of the results obtained from the catalytic reactions, it could be concluded that LaOOH was the possible active species and high surface area was important for the high catalytic activity. 相似文献
173.
Kamble Vinod Tribhuvannathji Muley Dnyanoba Baburao Atkore Sandeep Tukaram Dakore Sharad Digambarrao 《中国化学》2010,28(3):388-392
Fluoroboric acid supported on silica gel (HBF4‐SiO2) catalyzes efficiently the three component condensation of an aldehyde, a 1,3‐dicarbonyl compound and urea or thiourea to afford the corresponding 3,4‐dihydropyrimidin‐ 2(1H)‐ones and thiones in high yields. The ambient conditions, fast reaction rates, and excellent product yields are the important characteristics of this reaction. 相似文献
174.
175.
Dr. Huan‐Ming Huang Dr. Joseph J. W. McDouall Prof. Dr. David J. Procter 《Angewandte Chemie (International ed. in English)》2018,57(18):4995-4999
Radical anions generated from urea carbonyls by reductive electron transfer are exploited in carbon–carbon bond formation. New radical cyclizations of urea radical anions deliver complex nitrogen heterocycles and, depending upon the proton source used in the reactions, a chemoselective switch between reaction pathways can deliver two heterobicyclic scaffolds. A computational study has been used to investigate the selectivity of the urea radical processes. Furthermore, radical cyclization cascades involving urea radical anions deliver unusual spirocyclic aminal architectures. 相似文献
176.
Dan Zhang Le-Kai Hou Qiang Zhang Jia-Wei He Prof. Hong-Jian Feng Prof. Frank Würthner Prof. Xiao-Juan Yang Prof. Biao Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1414-1421
Charge-transfer (CT) complexes, formed by noncovalent bonding between electron-rich (donor, D) and electron-deficient (acceptor, A) molecules (or moieties) have attracted considerable attention due to their fascinating structures and potential applications. Herein, we demonstrate that anion coordination is a promising strategy to promote CT complex formation between anion-binding, electron-rich tris(urea) donor ligands (D) and electron-deficient viologen cation acceptors (A), which form co-crystals featuring infinite ⋅⋅⋅DADA⋅⋅⋅ or discrete (circular DADA or three-decker DAD) π-stacking interactions. These CT complexes were studied by X-ray diffraction, UV/Vis spectroscopy, electric conductivity measurements, charge displacement curve (CDC) calculations, and DFT computations. 相似文献
177.
Zhaolong Wang Yiming Hu Wenjun Liu Dr. Li Xu Dr. Meili Guan Dr. Yan Zhao Dr. Jian Bao Prof. Huaming Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(42):9382-9388
Hydrogen production by energy-efficient water electrolysis is a green avenue for the development of contemporary society. However, the oxygen evolution reaction (OER) and the urea oxidation reaction (UOR) occurring at the anode are impeded by the sluggish reaction kinetics during the water-splitting process. Consequently, it is promising to develop bifunctional anodic electrocatalysts consisting of nonprecious metals. Herein, a bifunctional CoMn layered double hydroxide (LDH) was grown on nickel foam (NF) with a 1D–2D–3D hierarchical structure for efficient OER and UOR performance in alkaline solution. Owing to the significant synergistic effect of Mn doping and heterostructure engineering, the obtained Co1Mn1 LDH/NF exhibits satisfactory OER activity with a low potential of 1.515 V to attain 10 mA cm−2. Besides, the potential of the Co1Mn1 LDH/NF catalyst for UOR at the same current density is only 1.326 V, which is much lower than those of its counterparts and most reported electrocatalysts. An urea electrolytic cell with a Co1Mn1 LDH/NF anode and a Pt–C/NF cathode was established, and a low cell voltage of 1.354 V at 10 mA cm−2 was acquired. The optimized strategy may result in promising candidates for developing a new generation of bifunctional electrocatalysts for clean energy production. 相似文献
178.
Roman Abrams Prof. Jonathan Clayden 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(28):11697-11703
We report tandem alkyl-arylations and phosphonyl-arylations of vinyl ureas by way of a photocatalytic radical-polar crossover mechanism. Addition of photoredox-generated radicals to the alkene forms a new C−C or C−P bond and generates a product radical adjacent to the urea function. Reductive termination of the photocatalytic cycle generates an anion that undergoes a polar Truce–Smiles rearrangement, forming a C−C bond. The reaction is successful with a range of α-fluorinated alkyl sodium sulfinate salts and diarylphosphine oxides as radical precursors, and the conformationally accelerated Truce–Smiles rearrangement is not restricted by the electronic nature of the migrating aromatic ring. Formally the reaction constitutes an α,β-difuctionalisation of a carbon–carbon double bond, and proceeds under mild conditions with visible light and a readily available organic photocatalyst. The products are α,α-diaryl alkylureas typically functionalized with F or P substituents that may be readily converted into α,α-diaryl alkylamines. 相似文献
179.
The enzyme soluble epoxide hydrolase (sEH) plays a central role in metabolism of bioactive lipid signaling molecules. The substrate-specific hydrolase activity of sEH converts epoxyeicosatrienoic acids (EETs) to less bioactive dihydroxyeicosatrienoic acids. EETs exhibit anti-inflammatory, analgesic, antihypertensive, cardio-protective and organ-protective properties. Accordingly, sEH inhibition is a promising therapeutic strategy for addressing a variety of diseases. In this review, we describe small molecule architectures that have been commonly deployed as sEH inhibitors with respect to angiogenesis, inflammation and cancer. We juxtapose commonly used synthetic scaffolds and natural products within the paradigm of a multitarget approach for addressing inflammation and inflammation induced carcinogenesis. Structural insights from the inhibitor complexes and novel strategies for development of sEH-based multitarget inhibitors are also presented. While sEH inhibition is likely to suppress inflammation-induced carcinogenesis, it can also lead to enhanced angiogenesis via increased EET concentrations. In this regard, sEH inhibitors in combination chemotherapy are described. Urea and amide-based architectures feature prominently across multitarget inhibition and combination chemotherapy applications of sEH inhibitors. 相似文献
180.
利用荧光猝灭法和动态光散射法测定尿素-水混合溶剂中牛血清白蛋白(BSA)与荧光素的结合距离和BSA的流体动力学半径, 并通过分析BSA和荧光素在BSA-尿素-水和荧光素-尿素-水三元体系以及BSA-荧光素-尿素-水四元体系中荧光光谱的变化, 探讨尿素与蛋白质分子在水溶液中相互作用的机理及其对蛋白质构象的影响. 结果显示, BSA的3个结构域在尿素-水混合溶剂中具有不同的稳定性, 其中结构域III在尿素-水混合溶剂中是不稳定的, 而结构域I和结构域II分别在尿素浓度大于3.0和4.0 mol8226;L-1的混合溶剂中发生去折叠. 试验发现, BSA结构域II在低于去折叠浓度的尿素-水混合溶剂中形成更为紧密的构象, 这一现象可以归因于尿素与BSA结合引起的“蛋白质粘稠效应” 相似文献