The Experts below are selected from a list of 711 Experts worldwide ranked by ideXlab platform
David A. Nagib - One of the best experts on this subject based on the ideXlab platform.
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multi component Heteroarene couplings via polarity reversed radical cascades
2019Co-Authors: Jeremy M. Lear, Quentin J. Buquoi, Kui Pan, Darsheed N Mustafa, David A. NagibAbstract:A multi-component radical addition strategy enables difunctionalization of alkenes with Heteroarenes and a variety of radical precursors, including N3, P(O)R2, and CF3. This unified approach for coupling diverse classes of electrophilic radicals and Heteroarenes to vinyl ethers allows for direct, vicinal C-C as well as C-N, C-P, and C-Rf bond formation.
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Heteroarene Phosphinylalkylation via a Catalytic, Polarity-Reversing Radical Cascade
2019Co-Authors: Quentin J. Buquoi, Jeremy M. Lear, David A. NagibAbstract:A polarity-reversing radical cascade strategy for alkene difunctionalization by vicinal C–C and C–P bond formation has been developed. This approach to concurrently adding phosphorus and a Heteroarene across an olefin is enabled by photocatalytic generation of electrophilic P-centered radicals. Upon chemoselective addition to an olefin, the resulting nucleophilic C-centered radical selectively combines with electrophilic Heteroarenes, such as pyridines. This multicomponent coupling scheme for phosphinylalkylation complements classic two-component methods for hydrophosphinylation of alkenes and C–H phosphinylation of arenes. Included competition and photoquenching experiments provide insight into the selectivity and mechanism of this polarity-reversal pathway
Feng-ling Qing - One of the best experts on this subject based on the ideXlab platform.
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Direct and Regioselective C–H Oxidative Difluoromethylation of Heteroarenes
2018Co-Authors: Sheng-qing Zhu, Yin-li Liu, Feng-ling QingAbstract:The difluoromethyl group (CF2H) is of great interest in the area of medicinal chemistry. However, the investigation of molecular scaffolds containing this group has been hampered by the limitation of synthetic methods for the introduction of CF2H into Heteroarenes. Herein we disclose a new strategy for the direct introduction of a difluoromethyl group into Heteroarenes via the copper-mediated C–H oxidative difluoromethylation of Heteroarenes with TMSCF2H. This mild and regioselective method enables the convenient synthesis of a range of difluoromethylated Heteroarenes in high yields. The usage of 9,10-phenanthrenequinone (PQ) as an oxidant is critical to the success of this new difluoromethylation reaction
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direct introduction of ethoxycarbonyldifluoromethyl group to Heteroarenes with ethyl bromodifluoroacetate via visible light photocatalysis
2013Co-Authors: Qingyu Lin, Feng-ling Qing, Lingling ChuAbstract:A mild and versatile approach for the direct introduction of ethoxycarbonyldifluoromethyl-group to Heteroarenes via visible-light photocatalysis has been developed. The new photoredox protocol has enabled the difluoromethylenation of Heteroarenes containi
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copper catalyzed direct c h oxidative trifluoromethylation of Heteroarenes
2012Co-Authors: Lingling Chu, Feng-ling QingAbstract:This article describes the copper-catalyzed oxidative trifluoromethylation of Heteroarenes and highly electron-deficient arenes with CF3SiMe3 through direct C–H activation. In the presence of catalyst Cu(OAc)2, ligand 1,10-phenanthroline and cobases tert-BuONa/NaOAc, oxidative trifluoromethylation of 1,3,4-oxadiazoles with CF3SiMe3 proceeded smoothly using either air or di-tert-butyl peroxide as an oxidant to give the corresponding trifluoromethylated 1,3,4-oxadiazoles in high yields. Di-tert-butyl peroxide was chosen as the suitable oxidant for oxidative trifluoromethylation of 1,3-azoles and perfluoroarenes. Cu(OH)2 and Ag2CO3 were the best catalyst and oxidant for direct oxidative trifluoromethyaltion of indoles. The optimum reaction conditions enable oxidative trifluoromethylation of a range of Heteroarenes that bear numerous functional groups. The prepared trifluoromethylated Heteroarenes are of importance in the areas of pharmaceuticals and agrochemicals. The preliminary mechanistic studies of these...
Jingsong You - One of the best experts on this subject based on the ideXlab platform.
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Rhodium(III)-Catalyzed Oxidative Cross-Coupling of Unreactive C(sp3)-H Bonds with C(sp2)-H Bonds.
2017Co-Authors: Guangying Tan, Jingsong YouAbstract:The development of the oxidative cross-coupling of unreactive C(sp3)–H bonds with (hetero)arene C(sp2)–H bonds is considerably appealing, yet conceptually and practically challenging. Here, we disclose the rhodium-catalyzed oxidative heteroarylation of unactivated C(sp3)–H bonds with Heteroarene C(sp2)–H bonds. This method provides a step-economic route to β-heteroarylated 2-ethylpyridine derivatives, which exhibits relatively broad substrate scope, high tolerance level of sensitive functional groups, and high selectivity. The protocol can also be extended to the coupling reaction between 8-methylquinoline derivatives and Heteroarenes.
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palladium ii catalyzed oxidative c h c h cross coupling of Heteroarenes
2010Co-Authors: Fan Yang, Dongbing Zhao, Song Qin, Jingbo Lan, Ge Gao, Jingsong YouAbstract:An efficient methodology for the synthesis of unsymmetrical biheteroaryl molecules has been developed via Pd(II)-catalyzed oxidative C−H/C−H cross-coupling of Heteroarenes. An inversion in reactivity and selectivity has been achieved successfully to perform the desired heterocoupling. This process allows the heterocoupling of not only electron-rich N-containing Heteroarenes (e.g., xanthines, azoles, and indolizines) but also electron-poor pyridine N-oxides with various thiophenes or furans.
Jeremy M. Lear - One of the best experts on this subject based on the ideXlab platform.
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multi component Heteroarene couplings via polarity reversed radical cascades
2019Co-Authors: Jeremy M. Lear, Quentin J. Buquoi, Kui Pan, Darsheed N Mustafa, David A. NagibAbstract:A multi-component radical addition strategy enables difunctionalization of alkenes with Heteroarenes and a variety of radical precursors, including N3, P(O)R2, and CF3. This unified approach for coupling diverse classes of electrophilic radicals and Heteroarenes to vinyl ethers allows for direct, vicinal C-C as well as C-N, C-P, and C-Rf bond formation.
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Heteroarene Phosphinylalkylation via a Catalytic, Polarity-Reversing Radical Cascade
2019Co-Authors: Quentin J. Buquoi, Jeremy M. Lear, David A. NagibAbstract:A polarity-reversing radical cascade strategy for alkene difunctionalization by vicinal C–C and C–P bond formation has been developed. This approach to concurrently adding phosphorus and a Heteroarene across an olefin is enabled by photocatalytic generation of electrophilic P-centered radicals. Upon chemoselective addition to an olefin, the resulting nucleophilic C-centered radical selectively combines with electrophilic Heteroarenes, such as pyridines. This multicomponent coupling scheme for phosphinylalkylation complements classic two-component methods for hydrophosphinylation of alkenes and C–H phosphinylation of arenes. Included competition and photoquenching experiments provide insight into the selectivity and mechanism of this polarity-reversal pathway
Elizabeth H Krenske - One of the best experts on this subject based on the ideXlab platform.
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ionic and neutral mechanisms for c h bond silylation of aromatic heterocycles catalyzed by potassium tert butoxide
2017Co-Authors: Shibdas Banerjee, Yunfang Yang, Ian D Jenkins, Yong Liang, Anton A Toutov, Wenbo Liu, David P Schuman, Robert H Grubbs, Brian M Stoltz, Elizabeth H KrenskeAbstract:Exploiting C–H bond activation is difficult, although some success has been achieved using precious metal catalysts. Recently, it was reported that C–H bonds in aromatic heterocycles were converted to C–Si bonds by reaction with hydrosilanes under the catalytic action of potassium tert-butoxide alone. The use of Earth-abundant potassium cation as a catalyst for C–H bond functionalization seems to be without precedent, and no mechanism for the process was established. Using ambient ionization mass spectrometry, we are able to identify crucial ionic intermediates present during the C–H silylation reaction. We propose a plausible catalytic cycle, which involves a pentacoordinate silicon intermediate consisting of silane reagent, substrate, and the tert-butoxide catalyst. Heterolysis of the Si–H bond, deprotonation of the Heteroarene, addition of the Heteroarene carbanion to the silyl ether, and dissociation of tert-butoxide from silicon lead to the silylated Heteroarene product. The steps of the silylation m...
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Ionic and Neutral Mechanisms for C–H Bond Silylation of Aromatic Heterocycles Catalyzed by Potassium tert-Butoxide
2017Co-Authors: Shibdas Banerjee, Yunfang Yang, Ian D Jenkins, Yong Liang, Anton A Toutov, Wenbo Liu, David P Schuman, Robert H Grubbs, Brian M Stoltz, Elizabeth H KrenskeAbstract:Exploiting C–H bond activation is difficult, although some success has been achieved using precious metal catalysts. Recently, it was reported that C–H bonds in aromatic heterocycles were converted to C–Si bonds by reaction with hydrosilanes under the catalytic action of potassium tert-butoxide alone. The use of Earth-abundant potassium cation as a catalyst for C–H bond functionalization seems to be without precedent, and no mechanism for the process was established. Using ambient ionization mass spectrometry, we are able to identify crucial ionic intermediates present during the C–H silylation reaction. We propose a plausible catalytic cycle, which involves a pentacoordinate silicon intermediate consisting of silane reagent, substrate, and the tert-butoxide catalyst. Heterolysis of the Si–H bond, deprotonation of the Heteroarene, addition of the Heteroarene carbanion to the silyl ether, and dissociation of tert-butoxide from silicon lead to the silylated Heteroarene product. The steps of the silylation mechanism may follow either an ionic route involving K+ and tBuO– ions or a neutral heterolytic route involving the [KOtBu]4 tetramer. Both mechanisms are consistent with the ionic intermediates detected experimentally. We also present reasons why KOtBu is an active catalyst whereas sodium tert-butoxide and lithium tert-butoxide are not, and we explain the relative reactivities of different (hetero)arenes in the silylation reaction. The unique role of KOtBu is traced, in part, to the stabilization of crucial intermediates through cation−π interactions
