The Experts below are selected from a list of 83880 Experts worldwide ranked by ideXlab platform
Paul Knochel - One of the best experts on this subject based on the ideXlab platform.
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Lewis Acid Directed Regioselective Metalations of Pyridazine.
Angewandte Chemie (International ed. in English), 2019Co-Authors: Moritz Balkenhohl, Konstantin Karaghiosoff, Harish Jangra, Tobias Lenz, Marian Ebeling, Hendrik Zipse, Paul KnochelAbstract:Mono- or bidentate boron Lewis Acids trigger a regioselective magnesiation or zincation of pyridazine in position C3 (ortho product) or C4 (meta product). The regioselectivity of the metalation was rationalized with the help of calculated pKa values of both pyridazine and pyridazine/Lewis Acid complexes.
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Lewis Acid triggered regioselective magnesiation and zincation of uracils uridines and cytidines
Organic Letters, 2016Co-Authors: Lydia Klier, Eider Aranzamendi, Dorothee Ziegler, Konstantin Karaghiosoff, Thomas Carell, Johannes Nickel, Paul KnochelAbstract:The Lewis Acid MgCl2 allows control of the metalation regioselectivity of uracils and uridines. In the absence of the Lewis Acid, metalation of uracil and uridine derivatives with TMPMgCl·LiCl occurs at the position C(5). In the presence of MgCl2, zincation using TMP2Zn·2LiCl·2MgCl2 occurs at the position C(6). This metalation method provides easy access to functionalized uracils and uridines. Using TMP2Zn·2LiCl·2MgCl2 also allows to functionalize cytidine derivatives at the position C(6).
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Lewis Acid triggered selective zincation of chromones quinolones and thiochromones application to the preparation of natural flavones and isoflavones
Journal of the American Chemical Society, 2012Co-Authors: Lydia Klier, Konstantin Karaghiosoff, Tomke Bresser, Tobias A Nigst, Paul KnochelAbstract:A Lewis Acid-triggered zincation allows the regioselective metalation of various chromones and quinolones. In the absence of MgCl2, a C(3) zincation is observed, whereas in the presence of MgCl2 or a related Lewis Acid, C(2) zincation occurs. Applications to a natural flavone, isoflavone, and quinolone are shown.
Xiaobo Wang - One of the best experts on this subject based on the ideXlab platform.
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reinforcing effect of Lewis Acid base interaction on the high temperature colloidal stability and tribological performance of lubricating grease
Journal of Industrial and Engineering Chemistry, 2017Co-Authors: Nan Xu, Weimin Li, Ming Zhang, Xiaobo WangAbstract:Abstract The high-temperature tribological performance of lithium grease is enhanced by addition of Lewis Acid borate ester, which could interact with Lewis base RCO2− of lithium 12-hydroxystearate (LHS, constitute the thickener fiber network of lithium grease) to form a Lewis Acid–base complex. Important details about the Lewis Acid–base complex and its reinforcing effect on the tribological performance are elucidated by means of SRV oscillating friction and wear tester (SRV), Fourier transformation infrared spectroscopy (FTIR), TGA–DSC, and rheological methods. The experimental results strongly suggest that there is a Lewis base–Acid interaction between the boron atom of borate ester or boric Acid and the oxygen atom of RCO2−. Lewis Acid centers can serve as second-level linking points to reinforce the strength of the thickener fiber network and further improve the colloidal stability of lubricating grease. Compared with pure LHS, the Lewis Acid–base complex displays higher thermal stability, allowing lithium grease to be applied to higher temperature. Because of the enhancement of thermal stability and colloidal stability, film-forming property under high temperature can be greatly improved, resulting in >15% friction and >95% wear reductions.
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Reinforcing effect of Lewis Acid–base interaction on the high-temperature colloidal stability and tribological performance of lubricating grease
Journal of Industrial and Engineering Chemistry, 2017Co-Authors: Nan Xu, Weimin Li, Ming Zhang, Xiaobo WangAbstract:Abstract The high-temperature tribological performance of lithium grease is enhanced by addition of Lewis Acid borate ester, which could interact with Lewis base RCO2− of lithium 12-hydroxystearate (LHS, constitute the thickener fiber network of lithium grease) to form a Lewis Acid–base complex. Important details about the Lewis Acid–base complex and its reinforcing effect on the tribological performance are elucidated by means of SRV oscillating friction and wear tester (SRV), Fourier transformation infrared spectroscopy (FTIR), TGA–DSC, and rheological methods. The experimental results strongly suggest that there is a Lewis base–Acid interaction between the boron atom of borate ester or boric Acid and the oxygen atom of RCO2−. Lewis Acid centers can serve as second-level linking points to reinforce the strength of the thickener fiber network and further improve the colloidal stability of lubricating grease. Compared with pure LHS, the Lewis Acid–base complex displays higher thermal stability, allowing lithium grease to be applied to higher temperature. Because of the enhancement of thermal stability and colloidal stability, film-forming property under high temperature can be greatly improved, resulting in >15% friction and >95% wear reductions.
Nan Xu - One of the best experts on this subject based on the ideXlab platform.
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reinforcing effect of Lewis Acid base interaction on the high temperature colloidal stability and tribological performance of lubricating grease
Journal of Industrial and Engineering Chemistry, 2017Co-Authors: Nan Xu, Weimin Li, Ming Zhang, Xiaobo WangAbstract:Abstract The high-temperature tribological performance of lithium grease is enhanced by addition of Lewis Acid borate ester, which could interact with Lewis base RCO2− of lithium 12-hydroxystearate (LHS, constitute the thickener fiber network of lithium grease) to form a Lewis Acid–base complex. Important details about the Lewis Acid–base complex and its reinforcing effect on the tribological performance are elucidated by means of SRV oscillating friction and wear tester (SRV), Fourier transformation infrared spectroscopy (FTIR), TGA–DSC, and rheological methods. The experimental results strongly suggest that there is a Lewis base–Acid interaction between the boron atom of borate ester or boric Acid and the oxygen atom of RCO2−. Lewis Acid centers can serve as second-level linking points to reinforce the strength of the thickener fiber network and further improve the colloidal stability of lubricating grease. Compared with pure LHS, the Lewis Acid–base complex displays higher thermal stability, allowing lithium grease to be applied to higher temperature. Because of the enhancement of thermal stability and colloidal stability, film-forming property under high temperature can be greatly improved, resulting in >15% friction and >95% wear reductions.
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Reinforcing effect of Lewis Acid–base interaction on the high-temperature colloidal stability and tribological performance of lubricating grease
Journal of Industrial and Engineering Chemistry, 2017Co-Authors: Nan Xu, Weimin Li, Ming Zhang, Xiaobo WangAbstract:Abstract The high-temperature tribological performance of lithium grease is enhanced by addition of Lewis Acid borate ester, which could interact with Lewis base RCO2− of lithium 12-hydroxystearate (LHS, constitute the thickener fiber network of lithium grease) to form a Lewis Acid–base complex. Important details about the Lewis Acid–base complex and its reinforcing effect on the tribological performance are elucidated by means of SRV oscillating friction and wear tester (SRV), Fourier transformation infrared spectroscopy (FTIR), TGA–DSC, and rheological methods. The experimental results strongly suggest that there is a Lewis base–Acid interaction between the boron atom of borate ester or boric Acid and the oxygen atom of RCO2−. Lewis Acid centers can serve as second-level linking points to reinforce the strength of the thickener fiber network and further improve the colloidal stability of lubricating grease. Compared with pure LHS, the Lewis Acid–base complex displays higher thermal stability, allowing lithium grease to be applied to higher temperature. Because of the enhancement of thermal stability and colloidal stability, film-forming property under high temperature can be greatly improved, resulting in >15% friction and >95% wear reductions.
Konstantin Karaghiosoff - One of the best experts on this subject based on the ideXlab platform.
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Lewis Acid Directed Regioselective Metalations of Pyridazine.
Angewandte Chemie (International ed. in English), 2019Co-Authors: Moritz Balkenhohl, Konstantin Karaghiosoff, Harish Jangra, Tobias Lenz, Marian Ebeling, Hendrik Zipse, Paul KnochelAbstract:Mono- or bidentate boron Lewis Acids trigger a regioselective magnesiation or zincation of pyridazine in position C3 (ortho product) or C4 (meta product). The regioselectivity of the metalation was rationalized with the help of calculated pKa values of both pyridazine and pyridazine/Lewis Acid complexes.
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Lewis Acid triggered regioselective magnesiation and zincation of uracils uridines and cytidines
Organic Letters, 2016Co-Authors: Lydia Klier, Eider Aranzamendi, Dorothee Ziegler, Konstantin Karaghiosoff, Thomas Carell, Johannes Nickel, Paul KnochelAbstract:The Lewis Acid MgCl2 allows control of the metalation regioselectivity of uracils and uridines. In the absence of the Lewis Acid, metalation of uracil and uridine derivatives with TMPMgCl·LiCl occurs at the position C(5). In the presence of MgCl2, zincation using TMP2Zn·2LiCl·2MgCl2 occurs at the position C(6). This metalation method provides easy access to functionalized uracils and uridines. Using TMP2Zn·2LiCl·2MgCl2 also allows to functionalize cytidine derivatives at the position C(6).
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Lewis Acid triggered selective zincation of chromones quinolones and thiochromones application to the preparation of natural flavones and isoflavones
Journal of the American Chemical Society, 2012Co-Authors: Lydia Klier, Konstantin Karaghiosoff, Tomke Bresser, Tobias A Nigst, Paul KnochelAbstract:A Lewis Acid-triggered zincation allows the regioselective metalation of various chromones and quinolones. In the absence of MgCl2, a C(3) zincation is observed, whereas in the presence of MgCl2 or a related Lewis Acid, C(2) zincation occurs. Applications to a natural flavone, isoflavone, and quinolone are shown.
Tamejiro Hiyama - One of the best experts on this subject based on the ideXlab platform.
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selective c 4 alkylation of pyridine by nickel Lewis Acid catalysis
ChemInform, 2011Co-Authors: Yoshiaki Nakao, Yuuya Yamada, Natsuko Kashihara, Tamejiro HiyamaAbstract:Direct C-4-selective addition of pyridine derivatives with various alkenes is achieved for the first time by a nickel/ Lewis Acid cooperative catalysis with an N-heterocyclic carbene ligand.
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selective c 4 alkylation of pyridine by nickel Lewis Acid catalysis
Journal of the American Chemical Society, 2010Co-Authors: Yoshiaki Nakao, Yuuya Yamada, Natsuko Kashihara, Tamejiro HiyamaAbstract:Direct C-4-selective addition of pyridine across alkenes and alkynes is achieved for the first time by nickel/Lewis Acid cooperative catalysis with an N-heterocyclic carbene ligand. A variety of substituents on both alkenes and pyridine are tolerated to give linear 4-alkylpyridines in modest to good yields. The addition across styrene, on the other hand, gives branched 4-alkylpyridines. A single example of C-4-selective alkenylation is also described.
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nickel Lewis Acid catalyzed cyanoesterification and cyanocarbamoylation of alkynes
Journal of the American Chemical Society, 2010Co-Authors: Yasuhiro Hirata, Akira Yada, Yoshiaki Nakao, Tamejiro Hiyama, Eiji Morita, Masato Ohashi, Sensuke OgoshiAbstract:Cyanoformates and cyanoformamides are found to add across alkynes by nickel/Lewis Acid (LA) cooperative catalysis to give beta-cyano-substituted acrylates and acrylamides, respectively, in highly stereoselective and regioselective manners. The resulting adducts serve as versatile synthetic building blocks through chemoselective transformations of the ester, amide, and cyano groups as demonstrated by the synthesis of typical structures of beta-cyano ester, beta-amino nitrile, gamma-lactam, disubstituted maleic anhydride, and gamma-aminobutyric Acid. The related reactions of cyanoformate thioester and benzoyl cyanide, on the other hand, are found to add across alkynes with decarbonylation in the presence of a palladium/LA catalyst.
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Hydrocarbamoylation of Unsaturated Bonds by Nickel/Lewis-Acid Catalysis
Journal of the American Chemical Society, 2009Co-Authors: Yoshiaki Nakao, Hiroaki Idei, Kyalo Stephen Kanyiva, Tamejiro HiyamaAbstract:Formamides are found to undergo addition reactions across alkynes and 1,3-dienes by nickel/Lewis Acid catalysis to give a variety of α,β- and β,γ-unsaturated amides with stereo- and regioselectivity. Intramolecular insertion reactions of olefins into the C−H bonds of formamides also proceed under similar conditions. The presence of Lewis Acid cocatalysts is crucial, and formamide coordination to the Lewis Acid is considered to be responsible for the activation of their formyl C−H bonds probably through oxidative addition to nickel(0).
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A Dramatic Effect of Lewis-Acid Catalysts on Nickel-Catalyzed Carbocyanation of Alkynes
Journal of the American Chemical Society, 2007Co-Authors: Yoshiaki Nakao, Shiro Ebata, Akira Yada, Tamejiro HiyamaAbstract:Lewis-Acid catalysts such as AlMe3, AlMe2Cl, and BPh3 significantly improve the efficiency of the nickel-catalyzed arylcyanation of alkynes. Electron-rich aryl cyanides, which exhibit poor reactivity in the absence of Lewis Acids, readily undergo the arylcyanation reaction under the newly disclosed conditions. Excellent chemoselectivity is observed for aryl cyanides having a chloro and bromo group, allowing a single-step preparation of the synthetic intermediate of P-3622, a squalene synthetase inhibitor. Moreover, the first examples of alkenyl- and alkylcyanation of alkynes have been achieved by the nickel−Lewis Acid dual catalyst.
