- Convenient Preparation and Functionalization of 2-Metallated Pentafluoropropenes
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The title compounds are prepared by metallation of CF3CH=CF2 with LDA or t-BuLi or by metallation of CF3CBr2CF3 with 2 equivalents of zinc.CF3C(ZnX)=CF2 undergoes halogenation, oxidative dimerization, allylation and acylation reactions. Key Words: vinyl organofluorine zinc reagent; organolithium; zinc; oxidative coupling; halogenation
- Morken, Peter A.,Lu, Hengyao,Nakamura, Akihiro,Burton, Donald J.
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- Consecutive Transformations of Tetrafluoropropenes: Hydrogermylation and Catalytic C?F Activation Steps at a Lewis Acidic Aluminum Fluoride
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Functionalization reactions of the refrigerants HFO-1234yf (2,3,3,3-tetrafluoropropene) and HFO-1234ze (1,3,3,3-tetrafluoropropene) were developed. The selectivity and reactivity towards CF3 groups of C?F activation reactions can be controlled by employing either a germane or a silane as the hydrogen source. Unique transformations were designed to accomplish consecutive hydrogermylation and C?F activation steps. This allowed for an unprecedented transformation of an olefinic C?F bond into a C?H bond by heterogeneous catalysis. These reactions are catalyzed by nanoscopic aluminum chlorofluoride (ACF) under very mild conditions.
- Mei?ner, Gisa,Kretschmar, Konrad,Braun, Thomas,Kemnitz, Erhard
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- Nb-doped variants of high surface aluminium fluoride: A very strong bi-acidic solid catalyst
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A niobium doped high surface aluminium fluoride (HS-AlF3) catalyst was prepared, using an approach in which niobium doped aluminium hydroxide fluoride obtained via reaction of aqueous HF with the respective metal alkoxides in isopropanol is further fluorinated under flow of CHClF2 at 200 °C. A comparable procedure was used to synthesize a Nb-free variant for comparison. Both catalysts exhibit very strong Lewis acidic surface sites which are capable to activate strong carbon-halogen bonds at room temperature, just as the classical high-surface AlF3 (HS-AlF3), obtained by reacting aluminium isopropoxide with anhydrous HF, does. The catalysts were characterized by elemental analysis, P-XRD, MAS NMR spectroscopy, N2 adsorption, NH3-TPD, and pyridine photoacoustic FT-IR spectroscopy. In contrast to previously reported niobium doped HS-AlF3, which was prepared using anhydrous HF, the doped catalyst obtained via this aqueous HF-route shows excellent performance both in the isomerization of 1,2-dibromohexafluoropropane, a reaction that occurs only in the presence of the strongest Lewis acids, and in the cyclization of citronellal to isopulegol, a reaction which requires both, Lewis and Br?nsted acid sites.
- Marshall, Clara Patricia,Scholz, Gudrun,Braun, Thomas,Kemnitz, Erhard
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p. 6834 - 6845
(2019/05/27)
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- Selective reduction of a C–Cl bond in halomethanes with Et3GeH at nanoscopic Lewis acidic Aluminium fluoride
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The selective activation of C–Cl bonds of hydrochlorofluoromethanes and chloromethanes at moderate reaction conditions using ACF in a combination with Et3GeH is presented. The reactions of the chloromethanes (CH3Cl, CH2Cl2, CHCl3 and CCl4) in the presence of Et3GeH and ACF as catalyst led to the activation of only one C–Cl bond resulting in the hydrodechlorination. Friedel-Crafts reactions with benzene as solvent are suppressed by Et3GeH. A selective hydrodechlorination of hydrochlorofluoromethanes was achieved, because a transformation of a C–F bond into a C–H bond by the combination of ACF with Et3GeH did not occur. Supporting PulseTA experiments illustrated the interaction between the solid catalyst and Et3GeH, the solvent benzene or CH2Cl2.
- Mei?ner, Gisa,Feist, Michael,Braun, Thomas,Kemnitz, Erhard
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p. 234 - 241
(2017/09/12)
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- PREPARATION OF HALOGEN AND HYDROGEN CONTAINING ALKENES OVER METAL FLUORIDE CATALYSTS
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Halogenated alkenes, especially fluorinated alkenes can be prepared from halogenated and fluorinated alkanes, respectively, by dehydrohalogenation or dehydrofluorination in the presence of a high-surface metal fluoride or oxifluoride. Preferably, trifluoroethylene, pentafluoropropene, tetrafluorobutenes or trifluorobutadiene are prepared. Aluminium fluoride is highly suitable. The metal fluoride or oxifluoride can be applied supported on a carrier.
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Page/Page column 20-21
(2009/03/07)
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- Synthesis of fluorovinylsalicylic acids and their derivatives
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Palladium-catalyzed cross-coupling of iodosalicylic acid derivatives with polyfluorovinyl zinc reagents provided the corresponding fluorovinyl-substituted salicylates.Methyl-5-(β,β)-difluorovinyl methyl salicylate was prepared by a Wittig reaction of the 5-formyl compound with the strongly nucleophilic ylide, .In one sequence, a fluorine-free benzofuran was obtained, instead of a difluorovinylsalicylate. - Keywords: Fluorovinylsalicylic acids; Wittig reaction; Benzofuran
- Filler, Robert,Lin, Shan,Zhang, Zhaoxu
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- Preparation of β,β-Difluoro-α-(trifluoromethyl)styrenes by Palladium-Catalyzed Coupling of Aryl Iodides with Pentafluoropropen-2-ylzinc Reagent
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Substituted aromatic iodides are functionalized by pentafluoropropen-2-ylzinc, CF3C(ZnX)=CF2 (X = Br, I, or CF2=CCF3-), in the presence of Pd(PPh3)4 to give the corresponding arenes in good yields.This is particularly attractive for the preparation of title styrenes substituted with groups such as -NO2 or CO2R, which are incompatible with organomagnesium reagents.The best yields of the title styrenes with electron-donating substituents were obtained in DMF.For electron-withdrawing substituents, the best results were achieved in triglyme.A correlation was observed between Hammett ? constants and 19F NMR chemical shifts (R = 0.93-0.99, n = 8) and 2JF-F coupling constants (R = 0.94, n = 8).
- Morken, Peter A.,Burton, Donald J.
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p. 1167 - 1172
(2007/10/02)
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