- Unexpected substituent effects in offset π-π stacked interactions in water
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We have measured the rotational barriers of meta- and para-substituted N-benzyl-2-(2-fluorophenyl)pyridinium bromides in aqueous solution by dynamic NMR as a model system for offset-stacking interactions in proteins. Because the benzyl ring can stack with
- Rashkin, Mark J.,Waters, Marcey L.
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Read Online
- Preparation method and application of aggregation-induced emission halogen modified platinum complex
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The invention discloses a preparation method and application of an aggregation-induced emission halogen modified platinum complex, and belongs to the field of phosphorescent materials. According to the invention, seven platinum complexes are synthesized by taking a halogen-modified 2-phenylpyridine derivative as a cyclometalated ligand and 1, 10-phenanthroline as an auxiliary ligand. The method for synthesizing the cyclometalated ligand from the complex through Suzuki cross-coupling reaction is environment-friendly, simple, convenient and efficient. Through modular design, the halogen-modifiedcyclometalated platinum complex can obtain a platinum complex with excellent aggregation-induced emission properties, and has important application value in the field of phosphorescent materials.
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Paragraph 0011; 0026-0028
(2020/12/05)
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- NHC-Copper Mediated Ligand-Directed Radiofluorination of Aryl Halides
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[18F]-labeled aryl fluorides are widely used as radiotracers for positron emission tomography (PET) imaging. Aryl halides (ArX) are particularly attractive precursors to these radiotracers, as they are readily available, inexpensive, and stable. However, to date, the direct preparation of [18F]-aryl fluorides from aryl halides remains limited to SNAr reactions between highly activated ArX substrates and K18F. This report describes an aryl halide radiofluorination reaction in which the C(sp2)-18F bond is formed via a copper-mediated pathway. Copper N-heterocyclic carbene complexes serve as mediators for this transformation, using aryl halide substrates with directing groups at the ortho position. This reaction is applied to the radiofluorination of electronically diverse aryl halide derivatives, including the bioactive molecules vismodegib and PH089.
- Sharninghausen, Liam S.,Brooks, Allen F.,Winton, Wade P.,Makaravage, Katarina J.,Scott, Peter J. H.,Sanford, Melanie S.
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supporting information
p. 7362 - 7367
(2020/08/19)
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- Photoarylation of Pyridines Using Aryldiazonium Salts and Visible Light: An EDA Approach
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A metal-free methodology for the photoarylation of pyridines, in water, is described giving 2 and 4-arylated-pyridines in yields up to 96percent. The scope of the aryldiazonium salts is presented showing important results depending on the nature and position of the substituent group in the diazonium salt, that is, electron-donating or electron-withdrawing in the ortho, meta, or para positions. Further heteroaromatics were also successfully photoarylated. Mechanistic studies and comparison between our methodology and similar metal-catalyzed procedures are presented, suggesting the occurrence of a visible-light EDA complex which generates the aryl radical with no need for an additional photocatalyst.
- Bartolomeu, Aloisio De A.,Brocksom, Timothy J.,De Oliveira, Kleber T.,No?l, Timothy,Silva, Rodrigo C.
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- Aryl-Fluoride Bond-Forming Reductive Elimination from Nickel(IV) Centers
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The treatment of pyridine- and pyrazole-ligated NiII σ-aryl complexes with Selectfluor results in C(sp2)-F bond formation under mild conditions. With appropriate design of supporting ligands, diamagnetic NiIV σ-aryl fluoride intermediates can be detected spectroscopically and/or isolated during these transformations. These studies demonstrate for the first time that NiIV σ-aryl fluoride complexes participate in challenging C(sp2)-F bond-forming reductive elimination to yield aryl fluoride products.
- Meucci, Elizabeth A.,Ariafard, Alireza,Canty, Allan J.,Kampf, Jeff W.,Sanford, Melanie S.
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p. 13261 - 13267
(2019/09/07)
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- Gold-Catalyzed C(sp2)?C(sp) Coupling by Alkynylation through Oxidative Addition of Bromoalkynes
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A gold(I)-catalyzed cascade cyclization–alkynylation of allenoates using alkynyl bromide to generate β-alkynyl-γ-butenolides was investigated. Whereas alkynyl iodides afforded significant amounts of the homo-coupling of two lactone units, alkynyl bromides led to a selective reaction, and a broad functional group tolerance was observed. Under the optimized reaction conditions, it was possible to directly synthesize a large range of β-alkynyl-γ-butenolides in moderate to good yields without the need for any external oxidant.
- Yang, Yangyang,Schie?l, Jasmin,Zallouz, Sirine,G?ker, Verena,Gross, Jürgen,Rudolph, Matthias,Rominger, Frank,Hashmi, A. Stephen K.
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supporting information
p. 9624 - 9628
(2019/07/05)
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- Enabling Catalytic Arene C-H Amidomethylation via Bis(tosylamido)methane as a Sustainable Formaldimine Releaser
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Addition of catalytic arene C-H to formaldimines has been enabled by Ru(II)-catalyzed amidomethylation with bis(tosylamido)methane as a catalytic formaldimine releaser. The new process provides an atom-efficient and sustainable solution to address the challenges of formaldimines in this type of transformation. Furthermore, new synthetic routes based on this catalytic system have been developed for step-efficient access to N-heterotricyclic core structures that are pharmaceutically relevant.
- Li, Zhong-Yuan,Chaminda Lakmal, Hetti Handi,Cui, Xin
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supporting information
p. 3735 - 3740
(2019/05/24)
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- Ruthenium-Catalyzed Reductive Cleavage of Unstrained Aryl-Aryl Bonds: Reaction Development and Mechanistic Study
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Cleavage of carbon-carbon bonds has been found in some important industrial processes, for example, petroleum cracking, and has inspired development of numerous synthetic methods. However, nonpolar unstrained C(aryl)-C(aryl) bonds remain one of the toughest bonds to be activated. As a detailed study of a fundamental reaction mode, here a full story is described about our development of a Ru-catalyzed reductive cleavage of unstrained C(aryl)-C(aryl) bonds. A wide range of biaryl compounds that contain directing groups (DGs) at 2,2′ positions can serve as effective substrates. Various heterocycles, such as pyridine, quinoline, pyrimidine, and pyrazole, can be employed as DGs. Besides hydrogen gas, other reagents, such as Hantzsch ester, silanes, and alcohols, can be employed as terminal reductants. The reaction is pH neutral and free of oxidants; thus a number of functional groups are tolerated. Notably, a one-pot C-C activation/C-C coupling has been realized. Computational and experimental mechanistic studies indicate that the reaction involves a ruthenium(II) monohydride-mediated C(aryl)-C(aryl) activation and the resting state of the catalyst is a η4-coordinated ruthenium(II) dichloride complex, which could inspire development of other transformations based on this reaction mode.
- Zhu, Jun,Chen, Peng-hao,Lu, Gang,Liu, Peng,Dong, Guangbin
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supporting information
p. 18630 - 18640
(2019/11/21)
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- A tetranuclear CuII2DyIII2 coordination cluster as a Suzuki (C-C) coupling reaction promoter
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The air-stable tetranuclear coordination cluster [CuII2DyIII2L4(NO3)2(CH3CN)2]·2(CH3CN), which can be obtained in high yield, promotes the Suzuki coupling reaction of phenylboronic acid with substituted aryl halides under environmentally benign conditions.
- Kumar, Prashant,Griffiths, Kieran,Anson, Christopher E.,Powell, Annie K.,Kostakis, George E.
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supporting information
p. 17202 - 17205
(2019/01/03)
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- Metallaphotoredox-Mediated Csp2-H Hydroxylation of Arenes under Aerobic Conditions
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The direct hydroxylation of 2-arylpyridines and 2-arylbenzothiazoles via the merger of organic photoredox and metal catalysis is reported where 4CzIPN is used as the visible-light photocatalyst and Pd(OAc)2 as the metal catalyst. This method has been employed to synthesize organic molecules exhibiting excited-state intramolecular proton transfer properties for generating tunable luminescence responses.
- Shah, Sk. Sheriff,Paul, Amrita,Bera, Manoranjan,Venkatesh, Yarra,Singh, N. D. Pradeep
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supporting information
p. 5533 - 5536
(2018/09/21)
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- Transition-Metal-Free Decarboxylative Arylation of 2-Picolinic Acids with Arenes under Air Conditions
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A facile, transition-metal-free, and direct decarboxylative arylation of 2-picolinic acids with simple arenes is described. The oxidative decarboxylative arylation of 2-picolinic acids with arenes proceeds readily via N-chloro carbene intermediates to afford 2-arylpyridines in satisfactory to good yields under transition-metal-free conditions. This new type of decarboxylative arylation is operationally simple and scalable and exhibits high functional-group tolerance. Various synthetically useful functional groups, such as halogen atoms, methoxycarbonyl, and nitro, remain intact during the decarboxylative arylation of 2-picolinic acids.
- Zhang, Xitao,Feng, Xiujuan,Zhou, Chuancheng,Yu, Xiaoqiang,Yamamoto, Yoshinori,Bao, Ming
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supporting information
p. 7095 - 7099
(2018/11/23)
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- Palladium-catalysed electrophilic aromatic C-H fluorination
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Aryl fluorides are widely used in the pharmaceutical and agrochemical industries, and recent advances have enabled their synthesis through the conversion of various functional groups. However, there is a lack of general methods for direct aromatic carbon-hydrogen (C-H) fluorination. Conventional methods require the use of either strong fluorinating reagents, which are often unselective and difficult to handle, such as elemental fluorine, or less reactive reagents that attack only the most activated arenes, which reduces the substrate scope. A method for the direct fluorination of aromatic C-H bonds could facilitate access to fluorinated derivatives of functional molecules that would otherwise be difficult to produce. For example, drug candidates with improved properties, such as increased metabolic stability or better blood-brain-barrier penetration, may become available. Here we describe an approach to catalysis and the resulting development of an undirected, palladium-catalysed method for aromatic C-H fluorination using mild electrophilic fluorinating reagents. The reaction involves a mode of catalysis that is unusual in aromatic C-H functionalization because no organometallic intermediate is formed; instead, a reactive transition-metal-fluoride electrophile is generated catalytically for the fluorination of arenes that do not otherwise react with mild fluorinating reagents. The scope and functional-group tolerance of this reaction could provide access to functional fluorinated molecules in pharmaceutical and agrochemical development that would otherwise not be readily accessible.
- Yamamoto, Kumiko,Li, Jiakun,Garber, Jeffrey A. O.,Rolfes, Julian D.,Boursalian, Gregory B.,Borghs, Jannik C.,Genicot, Christophe,Jacq, Jér?me,Van Gastel, Maurice,Neese, Frank,Ritter, Tobias
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p. 511 - 514
(2018/03/02)
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- Ruthenium-Catalyzed meta-Selective C?H Mono- and Difluoromethylation of Arenes through ortho-Metalation Strategy
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The first example for the ruthenium-catalyzed ligand-directed meta-selective C?H mono- and difluoromethylation is developed, affording a variety of new meta-mono- and difluoromethylated 2-phenylpyridines, 2-phenylpyrimidines, and 1-phenylpyrazoles in moderate-to-good yields. This new transformation exhibits broad substrate scope, good functional group tolerance, and high efficiency, and offers a practical approach to synthesize mono- and difluoromethylated arenes. Mechanistic studies indicate that a reaction pathway involving palladium-initiated radical species is involved in the catalytic cycle. The new dual catalytic system consisting of compatible ruthenium(II) and palladium(0) complexes enables the key processes of C?H activation and mono-/difluoromethyl-radical formation to occur and achieves the meta-selective functionalization efficiently. In addition, the present protocol can also be extended to non-fluoromethylation.
- Li, Zhong-Yuan,Li, Liang,Li, Qi-Li,Jing, Kun,Xu, Hui,Wang, Guan-Wu
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supporting information
p. 3285 - 3290
(2017/03/16)
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- Copper-mediated C-H cyanation of (hetero)arenes with ethyl (ethoxymethylene)cyanoacetate as a cyanating agent
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A copper-mediated direct C-H cyanation of (hetero)arenes with ethyl (ethoxymethylene)cyanoacetate as a safe cyanating agent has been successfully developed by using molecular oxygen as the oxidant. The reaction tolerates a variety of functional groups and provides a facile and efficient method for the synthesis of a wide range of (hetero)aryl nitriles.
- Qi, Chaorong,Hu, Xiaohan,Jiang, Huanfeng
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p. 7994 - 7997
(2017/07/22)
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- DIRECT PALLADIUM-CATALYZED AROMATIC FLUORINATION
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Provided herein are palladium complexes comprising a ligand of Formula (Α') and a ligand of Formula (B), wherein R1-R18 are as defined herein. The palladium complexes are useful in methods of fluorinating aryl and heteroaryl substrates. Further provided are compositions and kits comprising the palladium complexes.
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Paragraph 00212; 00213
(2017/09/27)
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- Visible light-induced aerobic C-N bond activation: A photocatalytic strategy for the preparation of 2-arylpyridines and 2-arylquinolines
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An efficient method for accessing arylpyridines and arylquinolines via visible light-induced aerobic C-N bond activation is described. The applicability of different kinds of simple ketones, easily available amines, and the use of air as the sole oxidant make this transformation very attractive.
- Hu, Bei,Li, Yuyuan,Dong, Wuheng,Xie, Xiaomin,Wan, Jun,Zhang, Zhaoguo
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p. 48315 - 48318
(2016/06/09)
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- A general access to organogold(III) complexes by oxidative addition of diazonium salts
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At room temperature under mild photochemical conditions, namely irradiation with a simple blue light LED, gold(i) chloro complexes of both phosphane and carbene ligands in combination with aryldiazonium salts afford arylgold(iii) complexes. With chelating P,N-ligands cationic six- or five-membered chelate complexes were isolated in the form of salts with weakly coordinating counter anions that were brought in from the diazonium salt. With monodentate P ligands or N-heterocyclic carbene ligands and diazonium chlorides neutral arylgold(iii) dichloro complexes were obtained. The coordination geometry was determined by X-ray crystal structure analyses of representative compounds, a cis arrangement of the aryl and the phosphane ligand at the square planar gold(iii) center is observed.
- Huang, Long,Rominger, Frank,Rudolph, Matthias,Hashmi, A. Stephen K.
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supporting information
p. 6435 - 6438
(2016/06/06)
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- Continuous-Flow Synthesis of Biaryls by Negishi Cross-Coupling of Fluoro- and Trifluoromethyl-Substituted (Hetero)arenes
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A continuous-flow method for the regioselective arylation of fluoroarenes and fluoropyridines has been developed. The telescoped procedure reported here consists of a three-step metalation, zincation, and Negishi cross-coupling sequence, providing efficient access to a variety of functionalized 2-fluorobiaryl products. Precise temperature control of the metalation step, made possible by continuous-flow technology, allowed for the efficient preparation of the arylated products in high yields and short residence times. Additionally, several examples of the regioselective arylation of benzotrifluoride derivatives are also provided.
- Roesner, Stefan,Buchwald, Stephen L.
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supporting information
p. 10463 - 10467
(2016/08/24)
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- Contrasting Anticancer Activity of Half-Sandwich Iridium(III) Complexes Bearing Functionally Diverse 2-Phenylpyridine Ligands
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We report the synthesis, characterization, and antiproliferative activity of 15 iridium(III) half-sandwich complexes of the type [(η5-Cp?)Ir(2-(R′-phenyl)-R-pyridine)Cl] bearing either an electron-donating (-OH, -CH2OH, -CH3) or electron-withdrawing (-F, -CHO, -NO2) group at various positions on the 2-phenylpyridine (2-PhPy) chelating ligand giving rise to six sets of structural isomers. The X-ray crystal structures of [(η5-Cp?)Ir(2-(2′-fluorophenyl)pyridine)Cl] (1) and [(η5-Cp?)Ir(2-(4′-fluorophenyl)pyridine)Cl] (2) exhibit the expected "piano-stool" configuration. DFT calculations showed that substituents caused only localized effects on the electrostatic potential surface of the chelating 2-PhPy ligand of the complexes. Hydrolysis of all complexes is rapid, but readily reversed by addition of NaCl. The complexes show preferential binding to 9-ethylguanine over 9-methyladenine and are active catalysts for the oxidation of NADH to NAD+. Antiproliferative activity experiments in A2780 ovarian, MCF-7 breast, A549 lung, and HCT116 colon cancer cell lines showed IC50 values ranging from 1 to 89 μM, with the most potent complex, [(η5-Cp?)Ir(2-(2′-methylphenyl)pyridine)Cl] (13) (A2780 IC50 = 1.18 μM), being 10× more active than the parent, [(η5-Cp?)Ir(2-phenylpyridine)Cl], and 2× more active than [(η5-CpxPh)Ir(2-phenylpyridine)Cl]. Intriguingly, contrasting biological activities are observed between structural isomers despite exhibiting similar chemical reactivity. For pairs of structural isomers both the nature and position of the functional group can affect the hydrophobicity of the complex. An increase in hydrophobicity resulted in enhanced cellular-iridium accumulation in A2780 ovarian cells, which generally gave rise to an increase in potency. The structural isomers [(η5-Cp?)Ir(2-(4′-fluorophenyl)pyridine)Cl] (2) and [(η5-Cp?)Ir(2-phenyl-5-fluoropyridine)Cl] (4) preferentially localized in the cytosol > membrane and particulate > nucleus > cytoskeleton. This work highlights the strong dependence of biological behavior on the nature and position of the substituent on the chelating ligand and shows how this class of organometallic anticancer complexes can be fine-tuned to increase their potency without using extended cyclopentadienyl systems. (Chemical Equation Presented).
- Millett, Adam J.,Habtemariam, Abraha,Romero-Canelón, Isolda,Clarkson, Guy J.,Sadler, Peter J.
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supporting information
p. 2683 - 2694
(2015/06/23)
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- Directed meta-Selective Bromination of Arenes with Ruthenium Catalysts
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A Ru-catalyzed direct C?H activation/meta-bromination of arenes bearing pyridyl, pyrimidyl, and pyrazolyl directing groups has been developed. A series of bromo aryl pyridines and pyrimidines have been synthesized, and further coupling reactions have also been demonstrated for a number of representative functionalized arenes. Preliminary mechanistic studies have revealed that this reaction may proceed through radical-mediated bromination when NBS is utilized as the bromine source. This type of transformation has opened up a new direction for the radical non-ipso functionalization of metal with regard to future C?H activation development that would allow the remote functionalization of aromatic systems.
- Yu, Qingzhen,Hu, Le'An,Wang, Yue,Zheng, Shasha,Huang, Jianhui
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supporting information
p. 15284 - 15288
(2016/01/25)
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- FLUORSCENT DYES WITH LARGE STOKES SHIFTS
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Herein are disclosed fluorescent dyes based around a framework for a ligand comprising a pyridyl group linked to a diaryl anilido unit. A variety of ligands based on this framework are disclosed. The ligands chelate to a BF2 center to produce the fluorescent dye. The disclosed dyes combine longer Stokes shifts (approximately 100 nm) with increased quantum yields. They are also photostable in aqueous and organic solutions for several hours. These dyes may be used in the labeling of biomolecules for bioimaging and assays. Also disclosed are methods for the synthesis of these dyes.
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Paragraph 0072
(2014/08/06)
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- Palladium-catalyzed coupling of polyfluorinated arenes with heteroarenes via C-F/C-H activation
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The first palladium-catalyzed coupling of 2-pyridyl-polyfluoroarenes and benzoxazole, thiazole, benzothiazole, benzoimidazole, oxazole or oxadiazole via a concurrent C-F/C-H activation is described. Initial mechanistic studies showed that C-F activation o
- Yu, Daohong,Lu, Long,Shen, Qilong
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supporting information
p. 940 - 943
(2013/03/29)
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- Noncatalytic pyridyl-directed alkylation and arylation carbon-fluorine bond of polyfluoroarenes with grignard reagents
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Cross-coupling reaction of polyfluoroarenes with Grignard reagents via pyridine-directed cleavage of C-F bond in the absence of metal catalysts was developed. A possible mechanism was suggested.
- Xiong, Yang,Wu, Jingjing,Xiao, Senhan,Xiao, Juan,Cao, Song
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p. 4599 - 4603
(2013/06/05)
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- Copper-catalyzed fluorination of 2-pyridyl aryl bromides
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Copper(i)-catalyzed cross-coupling of aryl halides is the subject of extensive interest in synthetic chemistry, but the related catalytic fluorination is unsuccessful. Herein, we have developed a novel copper-catalyzed fluorination of aryl bromides using AgF as the fluorine source. In this transformation a pyridyl directing group is essential for successful catalytic fluorination. A XANES/EXAFS study indicated that the presence of the pyridyl group is essential to stabilize the Cu(i) species and accelerate oxidative addition of the aryl bromide. Further mechanistic studies implicated a Cu(i/iii) catalytic cycle in this Cu(i)-catalyzed fluorination, and final aryl C-F bond formation possibly proceeds through an irreversible reductive elimination of the ArCu(iii)-F species. This rare report of catalytic fluorination by a copper catalyst provides a valuable foundation for further development of Cu(i)-catalyzed fluorination of aryl halides.
- Mu, Xin,Zhang, Hao,Chen, Pinhong,Liu, Guosheng
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p. 275 - 280
(2014/01/06)
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- Rhodium(I)-catalyzed direct carboxylation of arenes with CO2 via chelation-assisted C-H bond activation
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Rh-catalyzed direct carboxylation of unactivated aryl C-H bond under atmospheric pressure of carbon dioxide was realized via chelation-assisted C-H activation for the first time. Variously substituted and functionalized 2-arylpyridines and 1-arylpyrazoles underwent the carboxylation in the presence of the rhodium catalyst and a stoichiometric methylating reagent, AlMe 2(OMe), to give carboxylated products in good yields. The catalysis is proposed to consist of methylrhodium(I) species as the key intermediate, which undergoes C-H activation to afford rhodium(III), followed by reductive elimination of methane to give nucleophilic arylrhodium(I). This approach demonstrates promising application of C-H bond activation strategy in the field of carbon dioxide fixation.
- Mizuno, Hajime,Takaya, Jun,Iwasawa, Nobuharu
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supporting information; experimental part
p. 1251 - 1253
(2011/04/16)
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- Nickel-catalyzed Suzuki-Miyaura reaction of aryl fluorides
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Two protocols for the nickel-catalyzed cross-coupling of aryl fluorides with aryl boronic esters have been developed. The first employs metal fluoride cocatalysts, such as ZrF4 and TiF4, which enable Suzuki-Miyaura reactions of aryl fluorides bearing electron-withdrawing (ketones, esters, and CF3), aryl and alkenyl groups as well as those comprising fused aromatic rings, such as fluoronaphthalenes and fluoroquinolines. The second protocol employs aryl fluorides bearing ortho-directing groups, which facilitate the difficult C-F bond activation process via cyclometalation. N-heterocycles, such as pyridines, quinolines, pyrazoles, and oxazolines, can successfully promote cross-coupling with an array of organoboronic esters. A study into the substituent effects with respect to both coupling components has provided fundamental insights into the mechanism of the nickel-catalyzed cross-coupling of aryl fluorides.
- Tobisu, Mamoru,Xu, Tian,Shimasaki, Toshiaki,Chatani, Naoto
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supporting information; experimental part
p. 19505 - 19511
(2012/01/31)
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- Preparation and evaluation of sulfur-containing metal chelators
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With a view to probe the structure and function of G-protein coupled receptors the synthesis of functionalized 8-mercaptoquinoline derivatives and 2-(2-pyridyl)thiophenol was achieved. A fluorescence-based method for determining the affinity of these metal chelators toward zinc ions was developed.
- Clavier, Sylvain,Rist, ystein,Hansen, Stina,Gerlach, Lars-Ole,Hoegberg, Thomas,Bergman, Jan
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p. 4248 - 4253
(2007/10/03)
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- Phase-Transfer-Catalyzed Gomberg-Bachmann Synthesis of Unsymmetrical Biarenes: A Survey of Catalysts and Substrates
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Two problems have hindered the Gomberg-Bachmann (GB) and Pschorr reactions of arenediazonium cations: the instability of the arenediazonium salts and side reactions.Arenediazonium tetrafluoroborate and hexafluorophosphate salts can be prepared in high yield and purity and can be stored safely.Unfortunately, these salts are insoluble in most nonpolar organic solvents.Crown ether complexation or other phase-transfer (pt) catalytic methodology can ameliorate this situation, and reactions conducted by the approaches outlined herein often afforded coupling or cyclization products in high yield and corresponding purity.The use of crown ethers, quarternary 'onium salts, lipophilic carboxylic acid salts, and even the polar cosolvent acetonitrile increase the utility of the ptGB reaction dramatically.Sixty examples of couplings are reported along with an assessment of selectivities.A number of examples are also presented of phase-transfer-type Pschorr cyclizations.In the latter case, the use of potassium superoxide, KO2, is introduced to suppress indazole formation.
- Beadle, James R.,Korzeniowsky, Stephen H.,Rosenberg, David E.,Garcia-Slanga, Blanche J.,Gokel, George W.
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p. 1594 - 1603
(2007/10/02)
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