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51.
Inversion of Supramolecular Helicity in Oligo‐p‐phenylene‐Based Supramolecular Polymers: Influence of Molecular Atropisomerism
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Fátima Aparicio Belén Nieto‐Ortega Francisco Nájera Francisco J. Ramírez Juan T. López Navarrete Juan Casado Luis Sánchez 《Angewandte Chemie (International ed. in English)》2014,53(5):1373-1377
The helical organization of oligo‐p‐phenylene‐based organogelators has been investigated by atomic force microscopy, circular and vibrational circular dichroism, and Raman techniques. Whilst OPPs with more than two phenyl rings in the core self‐assemble into left‐handed helices, that with a biphenyl core shows an inversion of the supramolecular helicity depending on the formation conditions through the atropisomerism of the biphenyl central unit. The results presented herein outline a new example of kinetically controlled modulation of supramolecular helicity. 相似文献
52.
The acetylene equivalent (E)-1-benzenesulfonyl-2-(trimethylsilyl)ethylene is readily synthesized in a one-pot reaction, in excellent yield under very mild reaction conditions, via iodosulfonylation-dehydroiodination of vinyltrimethylsilane. 相似文献
53.
Diego A. Alonso Mónica Fuensanta C. Nájera Montserrat Varea 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1119-1131
Abstract The use of π-electron-deficient aryl sulfones, especially 3,5-bis(trifluoromethyl) phenyl alkyl sulfones (BTFP-sulfones) as soft nucleophiles, as caboxylic acid protecting group and in Julia–Kocienski olefination reactions is described. In the case of α-(arylsulfonyl)acetates dialkylation, reactions are performed under phase-transfer analysis (PTC) conditions using K 2 CO 3 as base. Esters derived from 2-(arylsulfonyl)ethanol can be deprotected using aqueous NaHCO 3 . Alkyl BTFP sulfones are coupled with carbonyl compounds using KOH or P4-t-Bu as bases to give the corresponding alkenes after Smiles rearrangement. 相似文献
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The recyclable chiral 2-aminobenzimidazole-derived organocatalyst 1f efficiently promotes the room temperature asymmetric conjugate addition of 1,3-diketones, β-ketoesters, and malonates to maleimide and N-substituted maleimides, affording the corresponding Michael adducts in excellent yields and enantioselectivities even at gram scale. 相似文献
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Jordi SalabertRosa María Sebastián Adelina Vallribera Anna RoglansCarmen Nájera 《Tetrahedron》2011,67(45):8659-8664
Fluorous aryl compounds are obtained through the arylation of different electron-rich and electron-poor olefins with an arenediazonium salt bearing a fully fluorinated octyl-ponytail at the para position. The Matsuda-Heck reactions are catalyzed by Pd(OAc)2 or 4-hydroxyacetophenone oxime-derived palladacycle as efficient sources of Pd nanoparticles, with loadings of 1 mol % Pd, at room temperature, in methanol and without the need to add external base. 相似文献
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Juan J. Nájera Ruth Wamsley Deborah J. Last Kimberley E. Leather Carl J. Percival Andrew B. Horn 《国际化学动力学杂志》2011,43(12):694-707
In this paper, a real‐time laboratory study of the heterogeneous oxidation reaction of gas‐phase ozone with anthracene on surface substrates by using infrared spectroscopy in two distinctly different experimental configurations is reported. One set of kinetic measurements was made by attenuated total internal reflection infrared (ATR‐IR) spectroscopy using approximately 75‐nm films of anthracene adsorbed on ZnSe, for which the reactive uptake coefficient was determined to be (2.0 ± 1.1) × 10?7. Using an aerosol flow tube coupled to an infrared spectrometer (AFT‐IR), similar measurements were made on (NH4)2SO4 (ammonium sulfate) aerosols coated with a 0.1‐μm film of anthracene. The aerosol kinetic results as a function of the ozone concentration are consistent with a Langmuir–Hinshelwood‐type mechanism, for which the ozone‐partitioning coefficient was K = (1.4 ± 1.7) × 10?16 cm3 molecule?1, and the maximum pseudo‐first‐order rate coefficient was kImax = (0.035 ± 0.016) s?1. Infrared spectroscopic and mass spectrometric analysis of the ozonolysis reaction in the bulk phase identified the main ozonolysis products as dihydroxyanthrones, 9,10‐endoperoxide–anthracene, 9,10‐anthraquinone, and anthrone. Larger products were also seen in the mass spectra, most likely the result of secondary product and oligomer formation. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 694–707, 2011 相似文献
59.
Rafael Chinchilla Carmen N jera Miguel Yus
Andreas Heumann
《Tetrahedron: Asymmetry》1990,1(12):A115-A125The DCC-esterification method has been used to kinetically resolve racemic mixtures of alcohols. With simple chiral carboxylic acids, such as O-aryl lactic acids, in the presence of various basic catalysts, mixtures of the enantiomerically enriched alcohols (e.e. <50%) and the corresponding esters (d.e.<70%) have been obtained. 相似文献
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Several dimeric Cinchona-alkaloid anthracenyldimethyl-derived ammonium salts, are used as organocatalysts in the enantioselective Michael addition reaction of cyclic β-keto esters to α,β-unsaturated carbonyl compounds, in the presence of diisopropylethylamine as a base (30 mol %), for the generation of enantiomerically enriched adducts bearing quaternary stereocenters. Quinine and quinidine-derived dimeric ammonium salts (1–10 mol %) afford the opposite and higher enantioselectivities of the corresponding adducts (up to 94% ee) in good yields (up to 98%). Substituted 2-alkoxycarbonyl-1-indanones are used as nucleophile precursors, as well as ethyl 2-oxocyclopentanecarboxylate and tert-butyl 2,5-dioxo-1-phenylpyrrolidine-3-carboxylate. These organocatalysts can be recovered at the end of the reaction by precipitation in ether and reused without any loss of activity. 相似文献