- Photochemical Selective Fluorination of Organic Molecules Using Mercury (II) Fluoride
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Organic compounds, such as triphenylacetic acid, triphenyl ethylene, and triethyl phosphite can be selectively fluorinated in dimethylsulfoxide/HgF2 solutions under UV-visible illumination.Product yields, determined by 19F-NMR, are essentially quantitative for the compounds studied, and in some cases a single fluorinated product is formed.
- Habibi, Mohammed H.,Mallouk, Thomas E.
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- Carbonyl Difluoride: a Versatile Fluorinating Reagent
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Carbonyl difluoride is a readily accessible reagent for introducing fluorine into molecules by oxidative addition to the central atom or by displacement of hydrogen from P-H, N-H, or C-H bonds.
- Gupta, O. D.,Shreeve, Jean'ne M.
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Read Online
- Halogen Transfer to Carbon Radicals by High-Valent Iron Chloride and Iron Fluoride Corroles
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High-valent iron halide corroles were examined to determine their reactivity with carbon radicals and their ability to undergo radical rebound-like processes. Beginning with Fe(Cl)(ttppc) (1) (ttppc = 5,10,15-tris(2,4,6-triphenylphenyl)corrolato3-), the new iron corroles Fe(OTf)(ttppc) (2), Fe(OTf)(ttppc)(AgOTf) (3), and Fe(F)(ttppc) (4) were synthesized. Complexes 3 and 4 are the first iron triflate and iron fluoride corroles to be structurally characterized by single crystal X-ray diffraction. The structure of 3 reveals an AgI-pyrrole (η2-π) interaction. The Fe(Cl)(ttppc) and Fe(F)(ttppc) complexes undergo halogen transfer to triarylmethyl radicals, and kinetic analysis of the reaction between (p-OMe-C6H4)3C?and 1 gave k = 1.34(3) × 103 M-1 s-1 at 23 °C and 2.2(2) M-1 s-1 at -60 °C, ΔHL = +9.8(3) kcal mol-1, and ΔSL = -14(1) cal mol-1 K-1 through an Eyring analysis. Complex 4 is significantly more reactive, giving k = 1.16(6) × 105 M-1 s-1 at 23 °C. The data point to a concerted mechanism and show the trend X = F- > Cl- > OH- for Fe(X)(ttppc). This study provides mechanistic insights into halogen rebound for an iron porphyrinoid complex.
- Farley, Geoffrey W.,Siegler, Maxime A.,Goldberg, David P.
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p. 17288 - 17302
(2021/11/17)
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- Alkali Metal Fluorides in Fluorinated Alcohols: Fundamental Properties and Applications to Electrochemical Fluorination
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Fundamental properties of alkali metal fluorides (MF, M = Cs, K) dissolved in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) or in 3,3,3-trifluoroethanol (TFE) are investigated, including solubility, conductivity, and viscosity. Solid-state structures of single crystals obtained from CsF/HFIP and CsF/TFE are described for the first time, giving insights into the multiple interactions between fluorinated alcohols and CsF. Applications in electrochemical fluorination reactions are successfully demonstrated.
- Shida, Naoki,Takenaka, Hiroaki,Gotou, Akihiro,Isogai, Tomohiro,Yamauchi, Akiyoshi,Kishikawa, Yosuke,Nagata, Yuuya,Tomita, Ikuyoshi,Fuchigami, Toshio,Inagi, Shinsuke
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supporting information
p. 16128 - 16133
(2021/07/26)
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- C(sp3)-H Fluorination with a Copper(II)/(III) Redox Couple
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Despite the growing interest in the synthesis of fluorinated organic compounds, few reactions are able to incorporate fluoride ions directly into alkyl C-H bonds. Here, we report the C(sp3)-H fluorination reactivity of a formally copper(III) fluoride complex. The C-H fluorination intermediate, LCuF, along with its chloride and bromide analogues, LCuCl and LCuBr, were prepared directly from halide sources with a chemical oxidant and fully characterized with single-crystal X-ray diffraction, X-ray absorption spectroscopy, UV-vis spectroscopy, and 1H nuclear magnetic resonance spectroscopy. Quantum chemical calculations reveal significant halide radical character for all complexes, suggesting their ability to initiate and terminate a C(sp3)-H halogenation sequence by sequential hydrogen atom abstraction (HAA) and radical capture. The capability of HAA by the formally copper(III) halide complexes was explored with 9,10-dihydroanthracene, revealing that LCuF exhibits rates 2 orders of magnitude higher than LCuCl and LCuBr. In contrast, all three complexes efficiently capture carbon radicals to afford C(sp3)-halogen bonds. Mechanistic investigation of radical capture with a triphenylmethyl radical revealed that LCuF proceeds through a concerted mechanism, while LCuCl and LCuBr follow a stepwise electron transfer-halide transfer pathway. The capability of LCuF to perform both hydrogen atom abstraction and radical capture was leveraged to enable fluorination of allylic and benzylic C-H bonds and α-C-H bonds of ethers at room temperature.
- Bower, Jamey K.,Cypcar, Andrew D.,Henriquez, Brenda,Stieber, S. Chantal E.,Zhang, Shiyu
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p. 8514 - 8521
(2020/05/28)
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- Fast Hydrocarbon Oxidation by a High-Valent Nickel–Fluoride Complex
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In the search for highly reactive oxidants we have identified high-valent metal–fluorides as a potential potent oxidant. The high-valent Ni–F complex [NiIII(F)(L)] (2, L=N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate) was prepared from [NiII(F)(L)]? (1) by oxidation with selectfluor. Complexes 1 and 2 were characterized by using 1H/19F NMR, UV-vis, and EPR spectroscopies, mass spectrometry, and X-ray crystallography. Complex 2 was found to be a highly reactive oxidant in the oxidation of hydrocarbons. Kinetic data and products analysis demonstrate a hydrogen atom transfer mechanism of oxidation. The rate constant determined for the oxidation of 9,10-dihydroanthracene (k2=29 m?1 s?1) compared favorably with the most reactive high-valent metallo-oxidants. Complex 2 displayed reaction rates 2000–4500-fold enhanced with respect to [NiIII(Cl)(L)] and also displayed high kinetic isotope effect values. Oxidative hydrocarbon and phosphine fluorination was achieved. Our results provide an interesting direction in designing catalysts for hydrocarbon oxidation and fluorination.
- Lovisari, Marta,McDonald, Aidan R.,Mondal, Prasenjit,Twamley, Brendan
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supporting information
p. 13044 - 13050
(2020/06/05)
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- Preparation method of fluoride and intermediate thereof (by machine translation)
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The invention discloses a preparation method of fluoride and an intermediate thereof. The preparation method comprises the following steps: in the presence of a basic reagent, the compound III and the thionyl fluoride are reacted in an organic solvent to obtain the compound of the formula I. The preparation method can obtain the fluorosulfite compound in a high yield, and has good functional group compatibility and substrate universality. (by machine translation)
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Paragraph 0206-0212
(2020/12/30)
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- Synthesis, Bonding, and Reactivity of Vanadium(IV) Oxido-Fluorido Compounds with Neutral Chelate Ligands of the General Formula cis-[VIV(=O)(F)(LN-N)2]+
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Reaction of the oxidovanadium(IV)-LN-N species (LN-N is bipy = 2,2′-bipyridine or bipy-like molecules) with either BF4- or HF and/or KF results in the formation of compounds of the general formula cis-[VIV(=O)(F)(LN-N)2]+. Structural and spectroscopic (electron paramagnetic resonance) characterization shows that these compounds are in the tetravalent oxidation state containing a terminal fluorido ligand. Density functional theory calculations reveal that the VIV-F bond is mainly electrostatic, which is reinforced by reactivity studies that demonstrate the nucleophilicity of the fluoride ligand in a halogen exchange reaction and in fluorination of various organic substrates.
- Passadis, Stamatis S.,Tsiafoulis, Constantinos,Drouza, Chryssoula,Tsipis, Athanassios C.,Miras, Haralampos N.,Keramidas, Anastasios D.,Kabanos, Themistoklis A.
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supporting information
p. 1364 - 1366
(2016/02/27)
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- Rearrangement in a Tripodal Nitroxide Ligand to Modulate the Reactivity of a Ti-F Bond
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The tripodal nitroxide ligand [(2-tBuNO)C6H4CH2)3N]3- (TriNOx3-) binds the Ti(IV) cation and prevents inner-sphere coordination of chloride in the complex [Ti(TriNOx)]Cl (1). The ligand undergoes an η2-NO to κ1-O rearrangement to enable a fluoride ion to bind in the related complex Ti(TriNOx)F (2). Computational and reactivity studies demonstrated that the ligand rearrangement contributed to the enthalpy change in the transfer of a fluoride anion.
- Boreen, Michael A.,Bogart, Justin A.,Carroll, Patrick J.,Schelter, Eric J.
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p. 9588 - 9593
(2015/10/12)
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- Photocatalyzed benzylic fluorination: Shedding "light" on the involvement of electron transfer
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The photocatalyzed oxidation of benzylic compounds by 1,2,4,5-tetracyanobenzene (TCB) in the presence of Selectfluor provides a synthetically efficient route to electron deficient, less substituted, and otherwise inaccessible benzylic fluorides. The virtue of this system is multifold: it is metal-free and mild, and the reagents are inexpensive. Mechanistically, the data suggest the intimate formation of intermediate radical cations in the key radical forming step, as opposed to a concerted hydrogen atom transfer process.
- Bloom, Steven,McCann, Michael,Lectka, Thomas
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supporting information
p. 6338 - 6341
(2015/01/16)
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- Electrochemical fluorination using alkali-metal fluorides
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Charged up: The selective electrochemical fluorination of organic compounds using the alkali-metal fluoride KF under very mild reaction conditions has been accomplished (see scheme). The long-standing problems of low solubility of metal fluorides in organic solvent and low nucleophilicity of fluoride ions for fluorination have been overcome by the use of of poly(ethylene glycol). Copyright
- Sawamura, Takahiro,Takahashi, Kohta,Inagi, Shinsuke,Fuchigami, Toshio
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supporting information; experimental part
p. 4413 - 4416
(2012/06/18)
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- Stable dialkyl ether/poly(hydrogen fluoride) complexes: Dimethyl ether/poly(hydrogen fluoride), a new, convenient, and effective fluorinating agent
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The preparation, 1H, 13C, and 19F NMR structural characterization as well as with DFT-based theoretical calculations of stable dialkyl ether/poly(hydrogen fluoride) complexes are reported. Dimethyl ether/poly(hydrogen fluoride) (DMEPHF), are stable complexes of particular interest and use. The DFT calculations, that are in agreement with NMR data, suggest a cyclic poly(hydrogen fluoride) bridged structure for DMEPHF. The complex, DME-5 HF was found to be a convenient and effective new fluorinating agent with the ease. of workup and applied to several fluorination reactions, such as the hydrofluorination and bromofluorination of alkenes, and fluorination of alcohols giving good to excellent yield with high selectivity. Homologous dialkyl ether/poly(hydrogen fluoride) (R2O/[HF]n R = Et, nPr) systems are also stable and suitable for fluorination reactions.
- Bucsi, Imre,Toeroek, Bela,Marco, Alfonso Iza,Rasul, Golam,Prakash, G. K. Surya,Olah, George A.
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p. 7728 - 7736
(2007/10/03)
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- Catalytic fluorination by halide exchange with 16-electron ruthenium(II) complexes. X-ray structure of [Tl(μ-F)2Ru(dppe)2]PF6
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The 16-electron ruthenium(II) complexes [RuCl(dppe)2]PF6 (2; dppe = 1,2-bis(diphenylphosphino)ethane), [RuCl(chiraphos)2]PF6 (3; chiraphos = (S,S)-3,4-bis(diphenylphosphino)butane), and [RuCl(PNNP)]PF6 (4; PNNP = (1S,2S)-N,N′-bis[2-(diphenylphosphino)-benzylidene]diaminocyclohexane) catalyze the nucleophilic fluorination of activated alkyl halides with a catalyst loading as low as 1 mol %. The alkyl halides (CH3)3CX (X = Br, 5c; X = I, 5d), Ph2CHBr (6c), and PhCH(Me)Br (7c) are converted to the fluoro analogues in the presence of TlF as the fluoride source. Yields are between 31 and 83%. The chiral complex 4 converts 7c to PhCH(Me)F (7a) with 49% yield after 24 h. At 1% conversion, 7a is nonracemic (16% ee), which indicates that kinetic resolution occurs, albeit at a low level. The fluorination of 1,2-dibromo-1,2,3,4-tetrahydronaphthalene (8c) is highly regioselective and gives 1-fluoro-2-bromo-1,2,3,4-tetrahydronaphthalene (8a) in 68% yield. The difluoro-bridged thallium adduct [Tl(μ-F)2Ru(dppe)2]PF6 (9) was observed by 31P NMR during catalysis with 2 and independently prepared by reaction of 2 with TlF (2 equiv). Complex 9 was characterized by 1H, 31P, 19F, and 205Tl NMR spectroscopy, as well as by X-ray diffraction.
- Barthazy, Peter,Togni, Antonio,Mezzetti, Antonio
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p. 3472 - 3477
(2008/10/08)
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- Polymerization of t-butyl vinyl ether mediated by an aluminum Lewis acid-TrF system and its complex structure-tacticity correlation
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A variety of aluminum (aryloxide)s were used with triphenylmethyl fluoride (TrF) initiator for the isoselective cationic polymerization of t-butyl vinyl ether. This contribution discusses the relationship between polymer tacticity and counteranion structure, which changed according to the bulkiness, strength and chirality of the Lewis acid combined with TrF so as to make the ionic pair more interactive in the polymerization process. Newly developed organoaluminum activators, 15 and 22, showed mm = 55-57%, which is a more than 10% increase in mm compared with achiral aluminum compounds.
- Oishi,Yamamoto
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p. 1445 - 1454
(2007/10/03)
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- Toward metal-mediated C-F bond formation. Synthesis and reactivity of the 16-electron fluoro complex [RuF(dppp)2]PF6 (dppp = 1,3-bis(diphenylphosphino)propane)
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The five-coordinate fluoro complex [RuF(dppp)2]PF6 (1a) has been prepared by reacting [RuCl(dppp)2]PF6 (1b) with TlF (dppp = 1,3-bis(diphenylphosphino)propane). An X-ray investigation of 1a shows a distorted trigonal bipyramidal geometry (Y-shaped). The 16-electron complex 1a reacts with a number of donors, including CO, H2, and F-. The X-ray structure of trans-[RuF(CO)(dppp)2]PF6 (2aBPh4) suggests that the π-donor ability of the fluoro ligand is only slightly higher than that of chloride. The reaction of 1a with [Me4N]F gives cis-[RuF2(dppp)2] (3), a rare difluoro complex not stabilized by π-acidic co-ligands. The Ru-F bond of 1a is hydrogenolyzed upon reaction with H2 to give [RuH(η2-H2)(dppp)2]+. The coordinatively unsaturated complex 1a reacts with activated haloalkanes R-X (X = Cl or Br) in 1:1 molar ratio to give the fluorinated organic derivative and [RuX(dppp)2]+. The halide metathesis proceeds instantaneously and quantitatively with (E)-3-bromo-1,3-diphenylpropene and chlorotriphenylmethane. Substrate conversion decreases with decreasing substitution at the halogen-bearing carbon atom.
- Barthazy,Stoop,Worle,Togni,Mezzetti
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p. 2844 - 2852
(2008/10/08)
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- Carbon-fluorine bond formation via a five-coordinate fluoro complex of ruthenium(II)
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The 16-electron, five-coordinate fluoro complex [RuF(dppp)2]PF6 (1a; dppp = propane-1,3-diylbis[diphenylphosphine] smoothly reacts with 1,3- diphenylallyl bromide (=1,1'-(3-bromoprop-1-ene-1,3-diyl)bis[benzne]) in dry CDCl3 to give 1,3-diphenylallyl fluoride and [RuBr(dppp)2]+ in nearly quantitative yield. Under similar conditions, bromide (or chloride)/fluoride exchange also occurs with chlorotriphenylmethane, bromodiphenylmethane, and tert-butyl bromide. The crystal structure of 1a is reported.
- Barthazy, Peter,Hintermann, Lukas,Stoop, Robert M.,Woerle, Michael,Mezzetti, Antonio,Togni, Antonio
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p. 2448 - 2453
(2007/10/03)
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- Fluorination process using hydrogen fluoride-containing fluorinating agents
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Fluorination processes using hydrogen fluoride-containing fluorinating agents that are safely and easily handled, transported, and stored and that also exhibit good reactivity are provided. More particularly, the invention provides processes for producing fluorinated products using fluorinating agents comprising hydrogen fluoride and a carrier that may be an acid salt or a water-soluble polymer.
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- Triphenylmethyl fluoride as a fluorinating agent in phosphorus-halogen chemistry
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Triphenylmethyl fluoride 1 will effect chlorine-fluorine exchange in certain phosphorus chlorides. Exchange of chlorine for fluorine was observed only in σ3λ3 (P)- and σ5λ5 (P)-compounds, while phosphorus oxychloride as an example of a σ4λ5 (P)-compound was unreactive towards 1.
- Plack, Volker,Goerlich, Jens R.,Schmutzler, Reinhard
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p. 173 - 176
(2007/10/03)
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- A facile synthesis of organofluorine compounds using a semi-molten mixture of tetrabutylammonium bromide and an alkali metal fluoride
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A semi-molten mixture of tetrabutylammonium bromide and an alkali metal fluoride (KF or CsF) has been found to be an efficient reagent system for the preparation of organofluorine compounds, e.g., CH3(CH2)7F, CH2=CH-CH2F, FCH2CO2C2H5, C6H5COF, and related compounds through facile fluoride-ion exchange with organohalides.The system provides a simple and convenient alternative to 'anhydrous' tetrabutylammonium fluoride for the synthesis of organofluorine compounds. - Keywords: Semi-molten mixture; Tetrabutylammonium bromide; Alkali metal fluorides; Organofluorine compounds; NMR spectroscopy
- Bhadury, Pinaki S.,Pandey, Mamta,Jaiswal, Devendra K.
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p. 185 - 188
(2007/10/02)
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- Evidence for Carbocation Intermediates in the TiO2-Catalyzed Photochemical Fluorination of Carboxylic Acids
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Laser flash photolysis/transient absorbance spectroscopy was used to determine the mechanism of photo-Kolbe fluorination of carboxylic acids, RCOOH --> RF, at colloidal TiO2 suspensions in acetonitrile.Transient absorption spectra of Ph3C(+), Ph3C(*), Ph2CH(*) and Ph2CH(+) were observed from the photooxidation of Ph3CCOOH and Ph2CHCOOH at TiO2 using 355-nm excitation.Transient decays, monitored in the presence and absence of fluoride ions, showed that the carbocations reacted rapidly with fluoride, but the neutral radicals did not.By varying the laser intensity, it wa s found that the photooxidation of Ph3CCOOH to Ph3C(*) at TiO2 occured via a single-photon process, while the formation of of Ph3C(+) required two photons.This finding is in agreement with the parabolic light intensity dependence of initial reaction rates in bulk photolysis experiments.Although fluoride is strongly adsorbed on the TiO2 surface in acetonitrile solution, the oxidizing power of photogenerated holes could be increased by coordinating HF to F(-), and therefore the threshold for oxidative photochemical fluorination was extented to more positive potentials.In this way less easily oxidized carboxylic acids RCOOH could be converted to RF.
- Lai, Cuiwei,Kim, Yeong Il,Wang, Chong Mou,Mallouk, Thomas E.
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p. 1393 - 1399
(2007/10/02)
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- Poly-4-vinylpyridinium poly(hydrogen fluoride): A solid hydrogen fluoride equivalent reagent
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Poly-4-vinylpyridinium poly(hydrogen fluoride) (PVPHF), containing 35-60% hydrogen fluoride by weight, was prepared as a solid hydrogen fluoride equivalent reagent. PVPHF with 60% hydrogen fluoride by weight was found to be a versatile fluorinating agent for the hydrofluorination and bromofluorination of alkanes and alkynes, fluorination of alcohols as well as other fluorination reactions. Low hydrogen fluoride content PVPHF (3 equivalents of hydrogen fluoride to 1 equivalent of 4-vinylpyridine unit) was also found to be an efficient reagent for bromofluorination of alkenes in the presence of 1,3-dibromo-5,5-dimethylhydrantoin. Fluorosulfonic acid-modified PVPHF showed enhanced reactivities for the fluorination of secondary alcohols.
- Olah,Li,Wang,Surya Prakash
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p. 693 - 699
(2007/10/02)
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- The effect of heteroatoms on the reactions of organic molecules with caesium fluoroxysulphate
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CsSO4F reacted at room temperature, or at 35°C in acetonitrile with various heteroatom-containing organic molecules, and three types of transformations have been observed. Fluoro substitution process took place with triphenylmethane, triphenylsilane, triphenylchlorosilane, 4-tert-butylphenol, benzaldehyde, and octanol, thus forming fluorotriphenylmethane, fluorotriphenylsilane, 2-fluoro-4-tert-butylphenol, benzoyl fluoride, or octanoyl fluoride in high yields. Substitution reaction was accompanied by fluoroaddition process in the case of 2-fluoro-4-tert-butylphenol, where 2,2-difluoro-4-tert-butylcyclohexadienon-4,6- was isolated. CsSO4F easily oxidised secondary alcohols to ketones, and 1,2-dihydro-4-tert-butylbenzene to quinone derivate. Oxygenation process was observed in the case of triphenylphosphine, and dibenzothiophene, while ethyl iodide was transformed to ethyliodo(III) difluoride. Solvent plays an important role in these reactions, being successfully performed in CH3CN, and completely inhibited in CH2Cl2, while different shapes of the effect on fluorination of various organic molecules were observed by altering solvent nature by successive mixing of CH3CN with CH2Cl2.
- Stavber,Zupan
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p. 5875 - 5882
(2007/10/02)
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- The reactions of copper-dibromodifluoromethane-amide systems with alcohols
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1,1,1-Trifluoro-2-arylethanes can be prepared by the trifluoromethyldehydroxylation of benzyl alcohols using the copper-dibromodifluoromethane-amide reaction system, although the yields are low.The mechanism of the reaction may involve chelation of the substrate to copper so that α-substituted benzyl alcohols and other alcohols are unreactive.
- Clark, James H.,McClinton, Martin A.,Blade, Robert J.
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p. 257 - 267
(2007/10/02)
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- Silica-Bound Sulfonic Acid Catalysts
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The catalytic activity of colloidal silica sulfonic acid for the hydrolyses of diazinon and triphenylmethyl fluoride was compared with that of silica gel sulfonic acids, gel and macroporous poly(styrenesulfonic acids), powdered and soluble Nafion, p-toluenesulfonic acid, and hydrochloric acid.For diazinon hydrolysis, the colloidal catalyst was only slighty less active than the soluble strong acid catalysts and 2.8 times more active than any of other heterogeneous catalysts.The silica gel and polymeric sulfonic acid catalysts had similar activities.For triphenylmethyl fluoride hydrolysis all of the catalysts were only weakly active.
- Badley, Rickey D.,Ford, Warren T.
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p. 5437 - 5443
(2007/10/02)
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- Facile Transformation of β-D-Ribofuranosyl Purines and Pyrimidines into Their Respective 3'-Deoxy-threo-pentofuranosyl Nucleosides
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Practical syntheses of 3'-deoxy-β-D-threo-pentofuranosyl-uracil, -cytosine, -adenine, and -guanine (3U, C, A, G) from the corresponding ribonucleosides by two one-pot reactions with readily accessible reagents are described.The key reactions are the selective 3'-O-methanesulphonylations of the ribonucleosides, the deoxygenative -hydride shift of the methanesulphonates, and the reduction of in situ generated 3'-deoxy-2'-keto nucleosides therefrom.
- Kawana, Masajiro,Nishikawa, Masahiro,Yamasaki, Noritsugu,Kuzuhara,Hiroyoshi
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p. 1593 - 1596
(2007/10/02)
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- Electrophilic Reactivity of the Triphenylmethyl Carbocation in Aqueous Solutions
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The triphenylmethyl (trityl) carbocation has been generated as a transient intermediate by laser flash photolysis of 1:2 (v/v) acetonitrile:water solutions of trityl acetate and trityl 4-cyanophenyl ether.Identification of the transient as the free carbocation in the ground state was based on its characteristic absorption spectrum and upon conductivity changes.Rate constants have been measured for the reaction of the cation in this solvent with a series of ionic and neutral nucleophiles.The solvent rate constant at 20 deg C is 1.5 x 105 s-1.Azide ions reacts at 4.1 x 109 M-1s-1; the directly measured azide:water ratio is compared to literature values determined by product analysis.Chloride ion reacts at 2 x 106 M-1 s-1; with bromide the equilibrium addition can be observed with k(comb) = 5 x 106 M-1 s-1 and k(ion) for Ph3CBr = 8 x 105 s-1.Rate constants do not adhere to the N+ relationship.This predicts a slope of unity in a plot of log k(Ph3C+) vs.N+, with the better nucleophiles reacting at the 1010 encounter-controlled limit.Azide is the only nucleophile of those studied to approach this.Sulfite and thiolate ions, which are better N+ nucleophiles, react at 2-3 x 108 M-1s-1, while amines react in the 106-107 M-1s-1 range.The plot vs.N+ has a slope of 0.3-0.4.One explanation is that rate constants for the better nucleophiles do level, but this occurs considerably below the 1010 limit.Alternatively, the less than unit slope is real and this more reactive cation, in contrast to more stable analogues, is exhibiting selectivity.
- McClelland, Robert A.,Banait, Narinder,Steenken, Steen
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p. 7023 - 7027
(2007/10/02)
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- Replecement of the carboxylic acid function with fluorine
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Replacement of a carbonyl function by fluorine, fluorodecarboxylation, is a new process that can be accomplished by the reaction of alkanoic acids with xenon difluoride.Primary, tertiary, and benzylic acids perform best in the reaction, which is conducted at room temperature in methylene chloride or chloroform solution.A reaction mechanism is proposed in which the acid is initially converted to a fluoroxenon ester, RCO2XeF.The esters of the primary and secondary acids react by nucleophilic displacement by fluoride, as evidenced by incorporation of 18F- and no reactions common to free radicals or carbocations.The esters of the tertiary and benzylic acids react by converting to free radicals that can be further oxidized to carbocations.Thus incorporation of 18F- and racemization are observed with α-methoxy-α-trifluoromethylphenylacetic acid.Hydroxyl and amino functions inhibit the reaction.Aromatic and vinylic acids do not react.
- Patrick, Timothy B.,Johri, Kamalesh K.,White, David H.,Bertrand, William S.,Mokhtar, Rodziah,et al.
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p. 138 - 141
(2007/10/02)
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- Fluorodecarboxylation with Xenon Difluoride
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The reaction between xenon difluoride and aliphatic carboxylic acids causes decarboxylation with replacement of the carboxyl group by fluorine.
- Patrick, Timothy B.,Johri, Kamalesh K.,White, David H.
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p. 4158 - 4159
(2007/10/02)
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