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Catalytic Conditions (catalytic + condition)
Selected AbstractsChemInform Abstract: Diversity-Oriented Synthesis of Quinolines via Friedlaender Annulation Reaction under Mild Catalytic Conditions.CHEMINFORM, Issue 25 2010D. Subhas Bose Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Some Aspects of Palladium-Catalyzed Cycloalkenylation: Developments of Environmentally Benign Catalytic Conditions and Demonstration of Tandem Cycloalkenylation.CHEMINFORM, Issue 39 2002Masahiro Toyota Abstract For Abstract see ChemInform Abstract in Full Text. [source] Mechanistic Insights into Acetophenone Transfer Hydrogenation Catalyzed by Half-Sandwich Ruthenium(II) Complexes Containing 2-(Diphenylphosphanyl)aniline , A Combined Experimental and Theoretical StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2008Alessia Bacchi Abstract Several new half-sandwich ruthenium(II) complexes containing 2-(diphenyphosphanyl)aniline (PNH2) of formula {Ru[(,2P,N)PNH2](p -cymene)Cl}Y [Y = Cl (1a), PF6 (1b), BF4 (1c), BPh4 (1d), TfO (1e)] were synthesized and fully characterized both in solution (1H NMR and 31P{1H} NMR spectroscopy) and in the solid state (FTIR, X-ray analysis on single crystal). Complexes 1a and 1b are active precatalysts in the hydrogen transfer reaction of acetophenone, leading to tof values up to 4440 h,1. In comparison, the {Ru[(,2P,N)PNMe2](p -cymene)Cl}Cl complex leads to a tof value of 100 h,1 under the same catalytic conditions. The mechanism through which the precatalysts operate was deeply explored by high-resolution MS (ESI) and DFT/PCM studies. The results reveal that the complexes containing PNH2 operate through a bifunctional mechanism analogous to that proposed for diamines and amino alcohol ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Enantioselective Ag-Catalyzed Allylation of Aldimines,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 30 2009Marina Naodovic Abstract A highly enantioselective synthesis of homoallylic amines, using allyltrimethoxysilane under AgI catalytic conditions, has been developed. Among the chiral ligands investigated, a remarkable difference in the resulting AgI complexes was observed. Under mild conditions and low catalyst loadings, homoallylamines were produced in high ee values (up to 80,%) and good yields. The methodology can be further extended to a diastere- and enantioselective crotylation of aldimines.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Mechanism of the Asymmetric Sulfoxidation in the Esomeprazole Process: Effects of the Imidazole Backbone for the EnantioselectionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Muthu Seenivasaperumal Abstract The asymmetric sulfoxidation reaction of imidazole-based prochiral sulfides was studied to explore the mechanistic details of the highly efficient esomeprazole process, which is one of the few industrial scale catalytic asymmetric procedures. The synthetic studies revealed that the smallest subunit governing the selectivity in the esomeprazole process is an imidazole ring. Thus, by using the esomeprazole procedure methyl imidazole sulfide could be oxidized as efficiently as its several functionalized derivatives, including pyrmetazol. However, alkylation of the imidazole nitrogen led to a major drop of the enantioselectivity. Our atmospheric pressure chemical ionization-mass spectrometry (APCI/MS) studies indicate that addition of small amounts of water to the reaction mixture facilitates the formation of mononuclear titanium species, which are the active catalytic intermediates of the selective oxidation reaction. One of the most important features of the esomeprazole procedure is that amine additives increase the enantioselectivity of the oxidation process. The NMR studies of the presumed reaction intermediates show that under catalytic conditions the amines are able to coordinate to titanium and dissociate the coordinated imidazole substrate. The density functional theory (DFT) modelling studies provided new insights in the mechanism of the asymmetric induction. It was found that the oxidation requires a lower activation energy if the imidazole sulfide precursor does not coordinate to titanium. Two possible reaction paths were explored for this out of sphere oxidation mechanism. The most important interaction governing the enantioselection is hydrogen bonding between the NH of the imidazole ring and the chiral tartrate ligand on titanium. Furthermore, the oxidation reaction imposes an important structural constraint to the TS structure involving a linear arrangement of the peroxide oxygens and the sulfur atom. This constraint and the N coordination of imidazole leads to a very strained structure for the inner sphere mechanism of the oxidation, which leads to a much higher activation barrier than the corresponding out of sphere process, and therefore it is unlikely. [source] Palladium-Catalyzed Intermolecular Three-Component Coupling of Organic Halides with Alkynes and Alkenes: Efficient Synthesis of Oligoene CompoundsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2007Kana Shibata Abstract The intermolecular three-component coupling of aryl or vinyl halides, diarylacetylenes, and monosubstituted alkenes effectively proceeds in the presence of palladium acetate, lithium chloride, and sodium bicarbonate as catalyst, promoter, and base, respectively, in aqueous DMF or DMSO to produce the corresponding 1,3-butadiene or 1,3,5-hexatriene derivatives. Use of dienyl bromides allows the coupling to afford 1,3,5,7-octatetraenes. Under the present catalytic conditions, fulvene derivatives are also formed efficiently by the 1:2 coupling of vinyl bromides and diarylacetylenes without adding the alkenes. [source] Convenient Preparation of Chiral ,,, -Epoxy Ketones via Claisen,Schmidt Condensation-Epoxidation SequenceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2007Yongcan Wang Abstract A novel Clasisen,Schmidt condensation-epoxidation sequence of aldehydes and ketones was developed to produce a series of chiral ,,, -epoxy ketones under asymmetric phase-transfer catalytic conditions. The organocatalytic method reported here can afford chiral ,,, -epoxy ketones under mild conditions with moderate to good yields and up to 96,% ee. [source] Asymmetric Sulfonium Ylide Mediated Cyclopropanation: Stereocontrolled Synthesis of (+)-LY354740CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006Varinder K. Aggarwal Prof. Abstract The reaction of ester-stabilized sulfonium ylides with cyclopentenone to give (+)- 5 ((1S,5R,6S)-ethyl 2-oxobicyclo[3.1.0]hexane-6-carboxylate), an important precursor to the pharmacologically important compound (+)-LY354740, has been studied using chiral sulfides operating in both catalytic (sulfide, Cu(acac)2, ethyl diazoacetate, 60,°C) and stoichiometric modes (sulfonium salt, base, room temperature). It was found that the reaction conditions employed had a major influence over both diastereo- and enantioselectivity. Under catalytic conditions, good enantioselectivity with low diastereoselectivity was observed, but under stoichiometric conditions low enantioselectivity with high diastereoselectivity was observed. When the stoichiometric reactions were conducted at high dilution, diastereoselectivity was reduced. This indicated that base-mediated betaine equilibration was occurring (which is slow relative to ring closure at high dilution). Based on this model, conditions for achieving high enantioselectivity were established as follows: use of a preformed ylide, absence of base, hindered ester (to reduce ylide-mediated betaine equilibration), and low concentration. Under these conditions high enantioselectivity (95,% ee) was achieved, albeit with low diastereocontrol. Our model for selectivity has been applied to other sulfonium ylide mediated cyclopropanation reactions and successfully accounts for the diastereoselectivity observed in all such reported reactions to date. [source] Chemical Tailoring of Porous Silica Xerogels: Local Structure by Vibrational SpectroscopyCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2004Alexandra Fidalgo Abstract Monolithic porous silica xerogels were synthesized by the sol,gel process, and their local structure was analysed by vibrational spectroscopy. The silica alcogels were prepared by a two-step hydrolytic polycondensation of tetraethoxysilane (TEOS) in isopropanol, with a water/TEOS molar ratio of 4. The hydrolysis step was catalysed by hydrochloric acid (HCl), with different HCl/TEOS molar ratios (ranging from 0.0005 to 0.009), and the condensation step was catalysed by ammonia (NH3), with different NH3/HCl molar ratios (ranging from 0.7 to 1.7). After appropriate ageing, the alcogels were washed with isopropanol and subcritically dried at atmospheric pressure. The diffuse reflectance infrared Fourier transform (DRIFT) spectra were analysed in terms of the main siloxane rings that form the silica particles, taking into account the splitting of the ,asSiOSi mode into pairs of longitudinal and transverse optic components, by long-range Coulomb interactions. It was proven that the proportion of residual silanol groups (which correlates with hydrophilicity), and the fraction of siloxane 6-rings (which correlates with porosity) may be tailored by adequate catalytic conditions, mostly by the hydrolysis pH. This was explained in terms of the reactions' mechanisms taking place in the two-step sol,gel process followed. [source] | ||||||||||