- Mild fluorination of chloropyridines with in situ generated anhydrous tetrabutylammonium fluoride
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This paper describes the fluorination of nitrogen heterocycles using anhydrous NBu4F. Quinoline derivatives as well as a number of 3- and 5-substituted pyridines undergo high-yielding fluorination at room temperature using this reagent. These results with anhydrous NBu4F compare favorably to traditional halex fluorinations using alkali metal fluorides, which generally require temperatures of ≥100 °C.
- Allen, Laura J.,Muhuhi, Joseck M.,Bland, Douglas C.,Merzel, Rachel,Sanford, Melanie S.
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p. 5827 - 5833
(2014/07/08)
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- Catalytic hydrodefluorination of fluoroaromatics with silanes as hydrogen source at a binuclear rhodium complex: Characterization of key intermediates
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Stoichiometric and catalytic hydrodefluorination reactions of fluorinated aromatic substrates on using [Rh(μ-H)(dippp)]2 (1) (dippp = 1,3-bis(diisopropylphosphino)propane) as catalyst and HSiEt3 as a hydrogen source are reported. Treatment of the hydrido complex 1 with the fluoroarenes gave the fluorido complex [Rh(μ-F)(dippp)]2 (2) and organic hydrodefluorination products. An unusual ortho-selectivity was observed in the reaction of 2,3,5,6-tetrafluoropyridine and pentafluorobenzene giving the 1,2-hydrodefluorinated products. The binuclear structure of complex 2 in the solid state was confirmed by X-ray diffraction. The fluorido complex 2 reacted with HSiEt3 and HSiiPr3 by elimination of the corresponding fluorosilanes to afford the η2-silane hydrido complexes [Rh(H)(η2-HSiEt3)(dippp)] (3) and [Rh(H)(η2-HSiiPr3)(dippp)] (4), respectively. The structures of the complexes 3 and 4 were derived from NMR data and DFT calculations. Catalytic reactions of pentafluoropyridine, 2,3,5,6-tetrafluoro- pyridine or 2,3,5,6-tetra-fluoropyridine, hexa- and pentafluorobenzene with HSiEt3 in the presence of 5 mol% of 1 afforded hydrodefluorination products with up to 19 turnovers after 48 h at 50 C. In contrast to the stoichiometric reactions, the catalytic transformations resulted predominantly in hydrodefluorinations at the para-position of the nitrogen atom in the heterocycles giving evidence for two different C-F activation pathways. Compound 3 can be considered to be an intermediate in the catalytic hydrodefluorinations of the fluoroarenes.
- Zámostná, Lada,Ahrens, Mike,Braun, Thomas
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p. 132 - 142
(2013/10/01)
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- The ionic liquid [bmim]Br as an alternative medium for the catalytic cleavage of aromatic C-F and C-Cl bonds
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The potential of [bmim]Br as an alternative to aprotic dipolar solvents in nickel-catalyzed hydrodehalogenation reactions is demonstrated. Hydrodechlorination of pentafluorochlorobenzene proceeds under the action of zinc in aqueous [bmim]Br. Under the above conditions aromatic C-F bonds also undergo slow cleavage. The reaction is significantly accelerated in the presence of nickel complexes with 2,2′-bipyridine or 1,10-phenanthroline. In the case of pentafluoroacetanilide highly regioselective ortho-hydrodefluorination leading to the formation of 3,4,5-trifluoroacetanilide is observed.
- Prikhod'ko, Sergey A.,Adonin, Nicolay Yu.,Parmon, Valentin N.
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scheme or table
p. 2265 - 2268
(2010/05/18)
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- Polyhalogenated heterocyclic compounds. Part 42. Fluorinated nitrogen heterocycles with unusual substitution patterns
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Reductive replacement of fluorine in 3,5-dichloro-2,4,6-trifluoropyridine 2a and pentafluoropyridine 2 using DIBAL and LAH leads to useful syntheses of fluoro and chlorofluoro pyridine derivatives. Replacement of fluorine by bromine using a mixture of HBr and AlBr3 is extremely efficient, giving excellent routes to 2,4,6-tribromo-3,5-difluoropyridine 3. Bromofluoro-pyrimidine and -quinoxaline derivatives have also been efficiently synthesised from perfluorinated precursors. Catalytic hydrogenation of bromofluoro heterocycles gives high yields of the corresponding fluorinated heterocycles. Reactions of nucleophiles with 3 gives surprising results. Soft nucleophiles, e.g. PhSNa displace bromine whereas hard nucleophiles, e.g. MeONa, displace fluorine. British Crown Copyright 1998, Defence Evaluation and Research Agency. Published by the Royal Society of Chemistry with the permission of the controller of Her Britannic Majesty's Stationery Office.
- Chambers, Richard D.,Hall, Christopher W.,Hutchinson, John,Millar, Ross W.
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p. 1705 - 1713
(2007/10/03)
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