- Immobilized bifunctional phosphonium salts as recyclable organocatalysts in the cycloaddition of CO2 and epoxides
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Several bifunctional phosphonium salt catalysts were prepared and immobilized on silica and polystyrene supports. The immobilized systems were compared with their homogeneous analogs in cyclic carbonate synthesis. Interestingly, in some cases, higher acti
- Steinbauer,Longwitz,Frank,Epping,Kragl,Werner
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p. 4435 - 4445
(2017/09/29)
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- Copper-Catalyzed Diastereoselective Synthesis of Trifluoromethylated Tetrahydrofurans
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The copper-catalyzed intramolecular diastereoselective trifluoromethylcycloetherification of homoallylic alcohols with Togni's reagent as trifluoromethylating reagent was realized under mild conditions. Various trifluoromethylated tetrahydrofurans were synthesized in moderate to good yields. Moreover, a wide range of common functional groups was tolerated.
- Wang, Yanan,Jiang, Min,Liu, Jin-Tao
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supporting information
p. 1322 - 1327
(2016/04/26)
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- Functionalized phosphonium-based ionic liquids as efficient catalysts for the synthesis of cyclic carbonate from expoxides and carbon dioxide
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A series of novel functionalized phosphonium-based ionic liquids (FPBILs) were synthesized by a simple method, and first evaluated as catalysts for the synthesis of cyclic carbonates through the cycloaddition of CO2 to epoxides in the absence of co-catalyst and solvent. The FPBILs perform well in the cycloaddition reaction, especially the carboxyl-functionalized one. Over [Ph3PC2H4COOH]Br, the yield of propylene carbonate is 97.3% (TOF = 64.9 h-1) at 130 C and 2.5 MPa in 3 h. The synergistic effects of polarization induced by hydrogen bonding and nucleophilic attack of Br-anion account for the excellent performance. Furthermore, the FPBILs with moderate methylene chain length show superior catalytic activity. It is because they have both strong acidity and weak electrostatic interaction between phosphonium cation and halide anion. The strong acidity facilitates the ring-opening of epoxyl, and the weak electrostatic interaction enhances the nucleophilic attack capability of Br -. It is envisaged that the metal- and solvent-free process has high potential for the catalytic conversion of CO2 into value-added chemicals.
- Dai, Wei-Li,Jin, Bi,Luo, Sheng-Lian,Luo, Xu-Biao,Tu, Xin-Man,Au, Chak-Tong
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p. 183 - 188
(2014/01/06)
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- Phosphonium salts and aldehydes from the convenient, anhydrous reaction of aryl acetals and triphenylphosphine hydrobromide
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The reactions of aryl acetals/ketals and triphenylphosphine hydrobromide gave the corresponding aldehydes/ketones and alkyl phosphonium bromides. This reaction was applied to convert acetals/ketals to the corresponding aldehydes/ketones under an anhydrous
- Ramanathan, Mani,Hou, Duen-Ren
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- Stereoselective 5-exo-trig radical cyclization in the enantioselective synthesis of Pregabalin
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A practical stereoselective 5-exo-trig radical cyclization procedure was developed in order to prepare enantiomerically pure GABA derivative precursors (4-alkyl-pyrrolidin-2-ones). This procedure allows much more rapid access to optically pure GABA derivatives, such as the powerful antiepileptic agent (S)-(+)-3-aminomethyl-5-methylhexanoic acid (Pregabaline).
- Rodríguez, Verónica,Quintero, Leticia,Sartillo-Piscil, Fernando
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p. 4305 - 4308
(2008/02/12)
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- Cascade rearrangement of spiroepoxymethyl radicals into 2-oxocycloalkyl radicals: Evaluation of a two-carbon cycloalkanone ring expansion
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Series of 2-bromomethyl- and 2-hydroxymethyl-1-oxaspiro[2.n]alkanes were prepared from cycloalkanones by initial Wadsworth-Horner-Emmons methodology to afford ester-substituted methylenecycloalkanes. The latter were selectively reduced to hydroxymethylmethylenecycloalkanes which were epoxidised with peroxyacetic acid. Homolytic reactions were studied by EPR spectroscopy which enabled transient 3-oxoalk-1-enyl radicals, and their cyclisation products, 2-oxocycloalkyl and 2-oxocycloalkylmethyl radicals, to be characterised. This evidence, together with end product analyses of organotin hydride reductions of the 2-bromomethyl-1-oxaspiro[2.n]alkanes, established that the initial spiroepoxymethyl radicals rearranged by a three-stage cascade of two consecutive β-scissions followed by a cyclisation. Cyclisations of the 3-oxoalk-1-enyl radicals took place mainly in the endo-mode to afford 2-oxocycloalkyl radicals, except for the 5-oxohept-6-enyl radical for which exo-cyclisation to generate the 2-oxocyclohexylmethyl radical was preferred. Kinetic data for the exo-and endo-cyclisations of the 4-oxohex-5-enyl radical were obtained from tributyltin hydride mediated reactions of 2-bromomethyl-1-oxaspiro[2.3]hexane.
- Afzal, Mohammad,Walton, John C.
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p. 937 - 945
(2007/10/03)
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- Investigation of Aliphatic Dienes by Chemical Ionization with Nitric Oxide
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It is shown that the position of the double bond close to the hydrocarbon end of an aliphatic diene functionalized at C(1) can readily be determined by chemical ionization with NO+.Owing to the low abundance of the ions characteristic for the position of the other double bond, its localization may be difficult.Measurement of the chemical ionization (nitric oxide as reagent gas) spectra of the corresponding epoxides or collision activation studies can help.
- Budzikiewicz, H.,Blech, St.,Schneider, B.
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p. 1057 - 1060
(2007/10/02)
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- THE SYNTHESIS OF (-)-SIRENIN, SPERM ATTRACTANT OF THE WATER MOLD ALLOMYCES MACROGYNUS
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Synthesis of (-)-sirenin 1a, sperm attracting hormone of Allomyces macrogynus was achieved through 10 steps from (-)-perillaldehyde 3.Formation of cyclopropane ring was executed diastereoselectively by the cyclization via intramolecular epoxide opening under carefully controlled condition.
- Kitahara, Takeshi,Horiguchi, Akira,Mori, Kenji
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p. 4713 - 4720
(2007/10/02)
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- THE 2-(DIPHENYLPHOSPHINO)ETHYL GROUP (DPPE) AS A NEW CARBOXYL-PROTECTING GROUP IN PEPTIDE CHEMISTRY
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The use of 2-(diphenylphosphino)ethyl group for carboxyl-protection of amino acids or peptides is described.This group is easily introduced by esterification using 2-(diphenylphosphino)ethanol in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine.These Dppe esters are stable under the standard conditions for peptide synthesis.Deprotection is carried out under mild conditions by quaternisation using methyl iodide followed by a β-elimination induced by fluoride ion or potassium carbonate.
- Chantreux, Dominique,Gamet, Jean-Paul,Jacquier, Robert,Verducci, Jean
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p. 3087 - 3094
(2007/10/02)
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