- The Origin of Catalytic Benzylic C?H Oxidation over a Redox-Active Metal–Organic Framework
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Selective oxidation of benzylic C?H compounds to ketones is important for the production of a wide range of fine chemicals, and is often achieved using toxic or precious metal catalysts. Herein, we report the efficient oxidation of benzylic C?H groups in a broad range of substrates under mild conditions over a robust metal–organic framework material, MFM-170, incorporating redox-active [Cu2II(O2CR)4] paddlewheel nodes. A comprehensive investigation employing electron paramagnetic resonance (EPR) spectroscopy and synchrotron X-ray diffraction has identified the critical role of the paddlewheel moiety in activating the oxidant tBuOOH (tert-butyl hydroperoxide) via partial reduction to [CuIICuI(O2CR)4] species.
- Carter, Joseph H.,Day, Sarah J.,Han, Xue,Kang, Xinchen,Kimberley, Louis,Li, Jiangnan,McInnes, Eric J. L.,Schr?der, Martin,Sheveleva, Alena M.,Smith, Gemma L.,Tang, Chiu C.,Tuna, Floriana,Yang, Sihai
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supporting information
p. 15243 - 15247
(2021/06/08)
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- Sequential Ir/Cu-Mediated Method for the Meta-Selective C-H Radiofluorination of (Hetero)Arenes
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This article describes a sequential Ir/Cu-mediated process for the meta-selective C-H radiofluorination of (hetero)arene substrates. In the first step, Ir-catalyzed C(sp2)-H borylation affords (hetero)aryl pinacolboronate (BPin) esters. The intermediate organoboronates are then directly subjected to copper-mediated radiofluorination with [18F]tetrabutylammonium fluoride to afford fluorine-18 labeled (hetero)arenes in high radiochemical yield and radiochemical purity. This entire process is performed on a benchtop without Schlenk or glovebox techniques and circumvents the need to isolate (hetero)aryl boronate esters. The reaction was automated on a TracerLab FXFN module with 1,3-dimethoxybenzene and a meta-tyrosine derivative. The products, [18F]1-fluoro-3,5-dimethoxybenzene and an 18F-labeled meta-tyrosine derivative, were obtained in 37 ± 5% isolated radiochemical yield and >99% radiochemical purity and 25% isolated radiochemical yield and 99% radiochemical purity, and 0.52 Ci/μmol (19.24 GBq/μmol) molar activity (Am), respectively.
- Wright, Jay S.,Sharninghausen, Liam S.,Preshlock, Sean,Brooks, Allen F.,Sanford, Melanie S.,Scott, Peter J. H.
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p. 6915 - 6921
(2021/05/29)
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- Trialkylammonium salt degradation: Implications for methylation and cross-coupling
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Trialkylammonium (most notably N,N,N-trimethylanilinium) salts are known to display dual reactivity through both the aryl group and the N-methyl groups. These salts have thus been widely applied in cross-coupling, aryl etherification, fluorine radiolabelling, phase-transfer catalysis, supramolecular recognition, polymer design, and (more recently) methylation. However, their application as electrophilic methylating reagents remains somewhat underexplored, and an understanding of their arylation versus methylation reactivities is lacking. This study presents a mechanistic degradation analysis of N,N,N-trimethylanilinium salts and highlights the implications for synthetic applications of this important class of salts. Kinetic degradation studies, in both solid and solution phases, have delivered insights into the physical and chemical parameters affecting anilinium salt stability. 1H NMR kinetic analysis of salt degradation has evidenced thermal degradation to methyl iodide and the parent aniline, consistent with a closed-shell SN2-centred degradative pathway, and methyl iodide being the key reactive species in applied methylation procedures. Furthermore, the effect of halide and non-nucleophilic counterions on salt degradation has been investigated, along with deuterium isotope and solvent effects. New mechanistic insights have enabled the investigation of the use of trimethylanilinium salts in O-methylation and in improved cross-coupling strategies. Finally, detailed computational studies have helped highlight limitations in the current state-of-the-art of solvation modelling of reaction in which the bulk medium undergoes experimentally observable changes over the reaction timecourse. This journal is
- Assante, Michele,Baillie, Sharon E.,Juba, Vanessa,Leach, Andrew G.,McKinney, David,Reid, Marc,Washington, Jack B.,Yan, Chunhui
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p. 6949 - 6963
(2021/06/02)
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- Metal triflates-methanesulfonic acid as new catalytic systems: Application to the Fries rearrangement
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A surprising synergistic effect has been discovered between metal triflates (Mg, Ca, Sc, Cu, Zn, Y, Ln, Bi) and methanesulfonic acid, leading to active catalytic systems for the Fries rearrangement. In particular, the systems based on yttrium and copper(II) triflate proved to be very active and much cheaper than scandium triflate. The efficiency of these systems might result from the catalytic Lewis acid activation of Br?nsted acids.
- Mouhtady, Omar,Gaspard-Iloughmane, Hafida,Roques, Nicolas,Le Roux, Christophe
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p. 6379 - 6382
(2007/10/03)
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- Demand-based thiolate anion generation under virtually neutral conditions: Influence of steric and electronic factors on chemo- and regioselective cleavage of aryl alkyl ethers
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Thiolate anions have been generated in a "demand-based" fashion under virtually neutral conditions for chemoselective deprotection of aryl alkyl ethers. Solvents play the critical role in making the reaction effective and should have high values of ε (>30), molecular polarizabilities (>10), and DN (>27) and low values of AN (>14). However, it is the combined effect of all of these physical properties that make a particular solvent effective. The reaction rates of cleavage of various aryl alkyl ethers are dependent on the steric crowding around the O-alkyl carbon and follow the order propargyl ≈ allyl ≈ benzyl > methyl > ethyl. Electron-withdrawing substituents increase the rate of ether cleavage reaction. The influence of the steric and electronic factors have been successfully exploited for selective deprotection of aryl alkyl ethers during inter- and intramolecular competitions.
- Chakraborti, Asit K.,Sharma, Lalima,Nayak, Mrinal K.
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p. 6406 - 6414
(2007/10/03)
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- The Catalytic Fries Rearrangement and o-Acylation Reactions Using Group 3 and 4 Metal Triflates as Catalysts
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Group 3 and 4 metal triflates (Sc(OTf)3, TiCl(OTf)3, Zr(OTf)4, and Hf(OTf)4) were found to be efficient catalysts in the Fries rearrangement of phenyl or 1 -naphthyl acylates. It was also found that the o-acylation (direct acylation) reactions of phenols and 1-naphthols with acid chlorides proceeded smoothly in the presence of the triflates. Both reactions were successfully carried out using small amounts of the triflates (catalytically), and comparison of catalytic activities of these metal triflates in these reactions is discussed.
- Kobayashi, Shue,Moriwaki, Mitsuhiro,Hachiya, Iwao
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p. 267 - 273
(2007/10/03)
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- Synthesis of Isoneobavachalcone and Analogues
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Isoneobavachalcone (I), a new C-formylated chalcone isolated from Psoralea coryfolia has been synthesised.In view of rare occurrence of C-formylated chalcones some analogues of I have also been synthesised.
- Sharma, V. K.,Gupta, S. R.
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p. 780 - 781
(2007/10/02)
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