- C2–H Arylation of Indoles Catalyzed by Palladium-Containing Metal-Organic-Framework in γ-Valerolactone
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An efficient and selective procedure was developed for the direct C2–H arylation of indoles using a Pd-loaded metal–organic framework (MOF) as a heterogeneous catalyst and the nontoxic biomass-derived solvent γ-valerolactone (GVL) as a reaction medium. The developed method allows for excellent yields and C-2 selectivity to be achieved and tolerates various substituents on the indole scaffold. The established conditions ensure the stability of the catalyst as well as recoverability, reusability, and low metal leaching into the solution.
- Anastasiou, Ioannis,Van Velthoven, Niels,Tomarelli, Elena,Lombi, Aurora,Lanari, Daniela,Liu, Pei,Bals, Sara,De Vos, Dirk E.,Vaccaro, Luigi
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p. 2786 - 2791
(2020/03/24)
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- NaNO2/K2S2O8-mediated Selective Radical Nitration/Nitrosation of Indoles: Efficient Approach to 3-Nitro- and 3-Nitrosoindoles
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JPZ acknowledges financial support from the National Natural Science Foundation of China (No. 21172163, 21472133), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and Key Laboratory of Organic Synthesis of Jiangsu Province (KJS1749). (Figure presented.).
- Shoberu, Adedamola,Li, Cheng-Kun,Tao, Ze-Kun,Zhang, Guo-Yu,Zou, Jian-Ping
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p. 2255 - 2261
(2019/04/13)
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- Mechanochemical Pd(II)-Catalyzed Direct and C-2-Selective Arylation of Indoles
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A mechanochemical method for the preparation of synthetically useful 2-arylindoles is developed using Pd(II) as the catalyst in the absence of phosphine ligands in a ball-mill. The developed protocol is highly C-2 selective and tolerant of structural variations with electron-rich and electron-deficient substituents both in indoles and iodoarenes. Arylation is possible in both unprotected indoles and N-protected indoles with the electron-donating group with the former substrate being relatively slower to react and little less yielding. Indoles with a deactivated five-membered ring could also take part in the reaction with ease. The scalability of the reaction was demonstrated by conducting the reaction in the gram scale. In general, the reactions were achieved in a shorter time than the conventional methods.
- Das, Dharmendra,Bhutia, Zigmee T.,Chatterjee, Amrita,Banerjee, Mainak
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p. 10764 - 10774
(2019/09/09)
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- Water-medium C-H activation over a hydrophobic perfluoroalkane-decorated metal-organic framework platform
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The use of water as reaction medium in the heterogeneous activation of C-H bonds has numerous advantages in terms of environmental benign, safety and cost efficiency impact. However, it is severely hampered because the reactants are difficult to dissolve in water and contact with the active sites of heterogeneous catalysts. Herein, we choose perfluoroalkane-functionalized mesoporous metal-organic framework (MOF) NU-1000 as a hydrophobic platform to encapsulate ultrafine palladium nanoparticles (Pd NPs) for C-H activation in water. The resultant Pd NPs stabilized by the perfluoroalkane exhibited high activity and regioselectivity in the direct C-H arylation of indoles in water. The introduction of perfluoroalkane chains into the mesoporous pores of NU-1000 provides hydrophobic surfaces to facilitate access of the reactants to the active sites to guarantee the high activity.
- Huang, Yuan-Biao,Shen, Min,Wang, Xusheng,Huang, Ping,Chen, Ruiping,Lin, Zu-Jin,Cao, Rong
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- A highly efficient and recyclable Fe3O4 magnetic nanoparticle immobilized palladium catalyst for the direct C-2 arylation of indoles with arylboronic acids
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A highly efficient Fe3O4 magnetic nanoparticle (MNP) immobilized palladium catalyst was prepared and applied to the direct C-2 arylation of indoles with arylboronic acids. The reactions generated the corresponding cross-coupling products in good yields. In addition, the supported catalyst with low loading (2.0 mol%) showed high stability and could be recovered and reused 8 times without significant loss of activity. The Royal Society of Chemistry 2014.
- Zhang, Lei,Li, Pinhua,Liu, Can,Yang, Jin,Wang, Min,Wang, Lei
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p. 1979 - 1988
(2014/06/24)
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- Palladium nanoparticles encapsulated in a metal-organic framework as efficient heterogeneous catalysts for direct C2 arylation of indoles
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Highly dispersed palladium nanoparticles (Pd NPs) encapsulated in the mesoporous cages of the metal-organic framework (MOF) MIL-101(Cr) have been prepared by using the wetness impregnation method. The Pd NPs were characterized by powder X-ray diffraction (PXRD), N2 adsorption, transmission electron microscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The particles size ((2.6 ± 0.5) nm) of the obtained Pd NPs was in good agreement with the cage diameters (2.9 and 3.4 nm) of the MOF. The resulting Pd/MIL-101(Cr) catalyst exhibited extremely high catalytic activities in the direct C2 arylation of substituted indoles by using only 0.1 mol-% of the Pd catalyst. Moreover, the catalyst is easily recoverable and can be reused several times without leaching into solution and loss of activity. The combination of the highly dispersible Pd NPs within the accessible mesoporous cages and the favorable adsorption of the aryl halides on MIL-101 are suspected to be the main reasons for the observed high activities of the Pd/MIL-101(Cr) catalyst in the direct C2 arylation of indoles. MOF-encapsulated catalyst: Highly dispersed palladium nanoparticles encapsulated in the mesoporous metal-organic framework (MOF) MIL-101(Cr) exhibited high catalytic activities for the direct C2 arylation of substituted indoles with a range of substituted iodobenzenes (see figure) by only using a very low amount of the Pd catalyst (0.1 mol-%). The catalyst is easily recovered and can be reused several times without leaching into solution and loss of activity.
- Huang, Yuanbiao,Lin, Zujin,Cao, Rong
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scheme or table
p. 12706 - 12712
(2011/12/04)
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- Fluorous silica gel-supported perfluoro-tagged palladium nanoparticles: An efficient and reusable catalyst for direct C-2 arylation of indoles
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The preparation of FSG-supported palladium nanoparticles and their application in direct C-2 arylation of indoles are presented. Moderate to good yields were obtained with ultra-low catalyst loading. The catalyst could be easily recovered by simple workup and reused up to seven runs with only a slight decrease in its activity. The Royal Society of Chemistry 2011.
- Wang, Liang,Yi, Wen-Bin,Cai, Chun
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supporting information; experimental part
p. 806 - 808
(2011/04/15)
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- Direct palladium-catalyzed C-2 and C-3 arylation of indoles: A mechanistic rationale for regioselectivity
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We have recently developed palladium-catalyzed methods for direct arylation of indoles (and other azoles) wherein high C-2 selectivity was observed for both free (NH)-indole and (NR)-indole. To provide a rationale for the observed selectivity ("nonelectrophilic" regioselectivity), mechanistic studies were conducted, using the phenylation of 1-methylindole as a model system. The reaction order was determined for iodobenzene (zero order), indole (first order), and the catalyst (first order). These kinetic studies, together with the Hammett plot, provided a strong support for the electrophilic palladation pathway. In addition, the kinetic isotope effect (KIEH/D) was determined for both C-2 and C-3 positions. A surprisingly large value of 1.6 was found for the C-3 position where the substitution does not occur (secondary KIE), while a smaller value of 1.2 was found at C-2 (apparent primary KIE). On the basis of these findings, a mechanistic interpretation is presented that features an electrophilic palladation of indole, accompanied by a 1,2-migration of an intermediate palladium species. This paradigm was used to design new catalytic conditions for the C-3 arylation of indole. In case of free (NH)-indole, regioselectivity of the arylation reaction (C-2 versus C-3) was achieved by the choice of magnesium base.
- Lane, Benjamin S.,Brown, Meghann A.,Sames, Dalibor
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p. 8050 - 8057
(2007/10/03)
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- Direct C-H bond arylation: Selective palladium-catalyzed C2-arylation of N-substituted indoles
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(Equation Presented) We present a new, practical method by which N-substituted indoles may be selectively arylated in the C2-position with good yields, low catalyst loadings, and a high degree of functional group tolerance. Our investigation found that two competitive processes, namely, the desired cross-coupling and biphenyl formation, were operative in this reaction. A simple kinetic model was formulated that proved to be instructive and provided useful guidelines for reaction optimization; the approach described within may prove to be useful in other catalytic cross-coupling processes.
- Lane, Benjamin S.,Sames, Dalibor
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p. 2897 - 2900
(2007/10/03)
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