排序方式: 共有91条查询结果,搜索用时 250 毫秒
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Steffen Fleischer Svenja Werkmeister Dr. Shaolin Zhou Dr. Kathrin Junge Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(29):9005-9010
Enantiomerically pure chiral amines are of increasing importance and commercial value in the fine chemical, pharmaceutical, and agrochemical industries. Here, we describe the straightforward synthesis of chiral amines by combining the atom‐economic and environmentally friendly hydroamination of alkynes with an enantioselective hydrogenation of in situ generated imines by using inexpensive hydrogen. By following this novel approach, a wide range of terminal alkynes can be reductively hydroaminated with primary amines including alkyl‐, and arylalkynes as well as aryl and heteroaryl amines. Excellent yields and selectivities up to 94 % ee and 96 % isolated yield were obtained. 相似文献
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Svenja Lowitzsch 《Numerical Algorithms》2005,39(1-3):253-256
Recently a new class of customized radial basis functions (RBFs) was introduced. We revisit this class of RBFs and derive a density result guaranteeing that any sufficiently smooth divergence-free function can be approximated arbitrarily closely by a linear combination of members of this class. This result has potential applications to numerically solving differential equations, such as fluid flows, whose solution is divergence free.
AMS subject classification 41Axx, 41A30, 41A35, 41A60Svenja Lowitzsch: The results are part of the authorss dissertation written at Texas A&M University, College Station, TX 77843, USA. 相似文献
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Cobalt‐Catalyzed Oxidase C−H/N−H Alkyne Annulation: Mechanistic Insights and Access to Anticancer Agents 下载免费PDF全文
Ruhuai Mei Hui Wang Svenja Warratz Prof. Stuart A. Macgregor Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6759-6763
Cp*‐free cobalt‐catalyzed alkyne annulations by C?H/N?H functionalizations were accomplished with molecular O2 as the sole oxidant. The user‐friendly oxidase strategy proved viable with various internal and terminal alkynes through kinetically relevant C?H cobaltation, providing among others step‐economical access to the anticancer topoisomerase‐I inhibitor 21,22‐dimethoxyrosettacin. DFT calculations suggest that electronic effects control the regioselectivity of the alkyne insertion step. 相似文献
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Dr. Simon T. R. Müller Tobias Hokamp Svenja Ehrmann Dr. Paul Hellier Prof. Dr. Thomas Wirth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(34):11940-11942
Ethyl diazoacetate (EDA) is one of the most prominent diazo reagents. It is frequently used in metal–carbene‐type reactions. However, EDA can also be used as a nucleophile under base catalysis. Whilst the addition of EDA to aldehydes can be performed using organic bases, the addition of EDA to other carbonyl electrophiles requires the use of organometallics such as lithium diisopropylamide (LDA). The generated ethyl lithiodiazoacetate is highly reactive and decomposes rapidly, even at low temperatures. Herein, we report a continuous flow protocol that overcomes the problems associated with the instantaneous decomposition of ethyl lithiodiazoacetate. The addition of ethyl lithiodiazoacetate to ketones provides direct access to tertiary diazoalcohols in good yields. 相似文献
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Ruthenium Oxidase Catalysis for Site‐Selective C–H Alkenylations with Ambient O2 as the Sole Oxidant 下载免费PDF全文
Alexander Bechtoldt Carina Tirler Keshav Raghuvanshi Svenja Warratz Christoph Kornhaaß Prof. Dr. Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2016,55(1):264-267
Ruthenium(II) oxidase catalysis by direct dioxygen‐coupled turnover enabled step‐economical oxidative C? H alkenylation reactions at ambient pressure. Versatile ruthenium(II) biscarboxylate catalysts displayed ample substrate scope and proved applicable to weakly coordinating and removable directing groups. The twofold C? H functionalization strategy was characterized by exceedingly mild reaction conditions as well as excellent positional selectivity. 相似文献
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Maya Kumari Sudip Kumar Bera Svenja Blickle Prof. Dr. Wolfgang Kaim Prof. Dr. Goutam Kumar Lahiri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(17):5461-5469
Epindolidione (H2L), a heteroatom-modified analogue of tetracene and a structural isomer of indigo, forms dinuclear complexes with [RuX2]2+, X=bpy (2,2′-bipyridine, [ 1 ]2+) or pap (2-phenylazopyridine, [ 2 ]2+), in its doubly deprotonated bridging form μ-L2−. The dications in compounds meso-[ 1 ](ClO4)2 and meso-[ 2 ](ClO4)2, [X2Ru(μ-L)RuX2](ClO4)2, contain five-membered chelate rings N-C−C-O-RuII with π bridged metals at an intramolecular distance of 7.19 Å. Stepwise reversible oxidation and reduction is mainly ligand centered (oxidation: L2−; reduction: X), as deduced from EPR of one-electron oxidized and reduced intermediates and from UV/Vis/NIR spectroelectrochemistry, supported by TD-DFT calculation results. The results for [ 1 ](ClO4)2 and [ 2 ](ClO4)2 are qualitatively similar to the ones observed with the deprotonated indigo-bridged isomers with their six-membered chelate ring structures, confirming the suitability of both π systems for molecular electronics applications, low-energy absorptions, and multiple electron transfers. 相似文献
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Fluorine substituents in organic molecules do dramatically influence the electronic structure of neighbouring functional groups and the conformation of molecules. Hence the presence of fluorine in a compound changes its chemical reactivity and biological activity. On the basis of MP2 and SCS-MP2 calculations, we discuss the conformational preferences and basicity of the diastereoisomeric 2-fluorocyclopropylamines (cis-2 and trans-2) in comparison to those of cyclopropylamine (1) and 2-fluoroethylamine (3). 1 and 2 are viewed as model compounds for the antidepressant drug tranylcypromine (trans-2-phenylcyclopropylamine, 1a) and its fluorinated derivatives 2. The potential energy profile for the rotation of the amino group in cis-2 differs from that of trans-2 and 1 which have very similar rotational curves. For 2 the global minimum conformer is trans-2a and the lowest energy cis-conformer 2c is less stable by 2.57 kcal mol(-1). The calculated enthalpy differences between the conformers gauche-1b and s-trans-1a (2.0 kcal mol(-1)) as well as between gauche-3b and gauche-4a (0.2 kcal mol(-1)) agree well with the available experimental data of 2.0 kcal mol(-1) and 0.1 +/- 0.3 kcal mol(-1), respectively. The calculated gas phase proton affinities (PA) of 1 (217.6 kcal mol(-1)), cis-2c (215.6 kcal mol(-1)), and trans-2a (209.3 kcal mol(-1)) follow the trends of the pKa values measured in solution for the diastereomeric 2-phenylcyclopropylamines 1a and 1b and their fluorinated derivatives cis-2 and trans-2. It is shown that the conformational preferences and basicity of the investigated molecules are due to stereoelectronic effects from hyperconjugative interactions which lead to different local charge distributions and different hybridization of the nitrogen lone-pair. The basicity of gauche-3a (PA = 215.3 kcal mol(-1)) and anti-3b (PA = 210.1 kcal mol(-1)) is controlled by the charge of the nitrogen atom, while that of cis-2c and trans-2a is overlap controlled as a result of different hybridization of the nitrogen lone-pair [sp4.34 (cis-2c), sp4.07 (trans-2a)]. 相似文献
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Ran Wang Yingjie Yu Dr. Meiyu Gai Dr. Ana Mateos-Maroto Dr. Svenja Morsbach Xiang Xia Maomao He Prof. Jiangli Fan Prof. Xiaojun Peng Prof. Katharina Landfester Prof. Shuai Jiang Prof. Wen Sun 《Angewandte Chemie (International ed. in English)》2023,62(44):e202308761
Enzymatic reactions can consume endogenous nutrients of tumors and produce cytotoxic species and are therefore promising tools for treating malignant tumors. Inspired by nature where enzymes are compartmentalized in membranes to achieve high reaction efficiency and separate biological processes with the environment, we develop liposomal nanoreactors that can perform enzymatic cascade reactions in the aqueous nanoconfinement of liposomes. The nanoreactors effectively inhibited tumor growth in vivo by consuming tumor nutrients (glucose and oxygen) and producing highly cytotoxic hydroxyl radicals (⋅OH). Co-compartmentalization of glucose oxidase (GOx) and horseradish peroxidase (HRP) in liposomes could increase local concentration of the intermediate product hydrogen peroxide (H2O2) as well as the acidity due to the generation of gluconic acid by GOx. Both H2O2 and acidity accelerate the second-step reaction by HRP, hence improving the overall efficiency of the cascade reaction. The biomimetic compartmentalization of enzymatic tandem reactions in biocompatible liposomes provides a promising direction for developing catalytic nanomedicines in antitumor therapy. 相似文献