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Hetero
Terms modified by Hetero Selected AbstractsBiocatalytic Racemization of (Hetero)Aryl-aliphatic ,-Hydroxycarboxylic Acids by Lactobacillus spp.EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2006Proceeds via an Oxidation, Reduction Sequence Abstract The biocatalytic racemization of a range of (hetero)aryl- and (di)aryl-aliphatic ,-hydroxycarboxylic acids has been achieved by using whole resting cells of Lactobacillus spp. The essentially mild (physiological) reaction conditions ensure the suppression of undesired side reactions, such as elimination, decomposition or condensation. Cofactor/inhibitor studies using a cell-free extract of Lactobacillus paracasei DSM 20207 reveal that the addition of redox cofactors (NAD+/NADH) leads to a distinct increase in the racemization rate, while strong inhibition is observed in the presence of Thio-NAD+, which suggests that the racemization proceeds by an oxidation,reduction sequence rather than involvement of a "racemase" enzyme. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Generation of a Small Library of Highly Electron-Rich 2-(Hetero)Aryl-Substituted Phenethylamines by the Suzuki,Miyaura Reaction: A Short Synthesis of an Apogalanthamine AnalogueEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2004Prasad Appukkuttan Abstract The Suzuki,Miyaura reaction is presented as a versatile procedure for the synthesis of a small library of highly electron-rich 2-[4,5-dimethoxy-2-(hetero)arylphenyl]ethylamines. Microwave-irradiation accelerates the reaction tremendously and furnishes superior yields. The difficult oxidative addition of the catalyst to a highly electron-rich and ortho -substituted system could be performed easily, and the proto-deboronation during cross-coupling reactions involving the highly electron-withdrawing (2-formylphenyl)boronic acid could be minimized. Enhanced yields and complete compatibility with aqueous conditions were found. This strategy was developed en route towards the synthesis of an apogalanthamine analogue. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of Novel Polycyclic Indole-Annulated Thiopyranocoumarin Derivatives via Domino Knoevenagel,Hetero- Diels,Alder Reaction in Aqueous MediaHELVETICA CHIMICA ACTA, Issue 5 2010Firouz, Matloubi Moghaddam Abstract An efficient synthesis of polycyclic indole derivatives is achieved via domino Knoevenagel,hetero- Diels,Alder reaction of O -acrylated salicylaldehyde derivatives with dihydroindole-2-thiones in H2O as solvent. The products are formed in good-to-excellent yields with high regio- and stereoselectivity. [source] Reactivity and Selectivity of Captodative Olefins as Dienes in Hetero -Diels,Alder ReactionsHELVETICA CHIMICA ACTA, Issue 10 2008Rubén Sanabria Abstract The reactivity and selectivity of the the captodative olefins 1-acylvinyl benzoates 1a,1f and 3a as heterodienes in hetero -Diels,Alder reactions in the presence of electron-rich dienophiles is described. Heterodienes 1 undergo regioselective cycloaddition with the alkyl vinyl etherdienophiles 6a,b and 9 to give the corresponding dihydro-2H -pyrans 7, 8, and 10 under thermal conditions. The reactivity of these cycloadditions depends, to a large extent, on the electronic demand of the substituent in the aroyloxy group of the heterodiene. Frontier-molecular-orbital (FMO; ab initio) and density-functional-theory (DFT) calculations of the ground and transition states account for the reactivity and regioselectivity observed in these processes. [source] Hetero-,-systems from 2 + 2 cycloreversion, part 2.1Ab initio thermochemical study of heterocyclobutanes 2 + 2 cycloreversion to form heteroethenes H2C=X (X=NH, O, SiH2, PH, S),HETEROATOM CHEMISTRY, Issue 7 2007Leonid E. Gusel'nikov Ab initio and DFT thermochemical study of diradical mechanism of 2 + 2 cycloreversion of parent heterocyclobutanes and 1,3-diheterocyclobutanes, cyclo -(CH2CH2CH2X), and cyclo -(CH2XCH2X), where X = NH, O, SiH2, PH, S, was undertaken by calculating closed-shell singlet molecules at three levels of theory: MP4/6-311G(d)//MP2/6-31G(d)+ZPE, MP4/6-311G(d,p)//MP2/6-31G (d,p)+ZPE, and B3LYP/6-311+G(d,p)+ZPE. The enthalpies of 2 + 2 cycloreversion decrease on going from group 14 to group 16 elements, being substantially higher for the second row elements. Normally endothermic 2 + 2 cycloreversion is predicted to be exothermic for 1,3-diazetidine and 1,3-dioxtane. Strain energies of the four-membered rings were calculated via the appropriate homodesmic reactions. The enthalpies of ring opening via the every possible one-bond homolysis that results in the formation of the corresponding 1,4-diradical were found by subtracting the strain energies from the central bond dissociation energies of the heterobutanes CH3CH2,CH2XH, CH3CH2,XCH3, and HXCH2,XCH3. The latter energies were determined via the enthalpies of the appropriate dehydrocondensation reactions, using C,H and X,H bond energies in CH3XH calculated at G2 level of theory. Except 1,3-disiletane, in which ring-opening enthalpy attains 69.7 kcal/mol, the enthalpies of the most economical ring openings do not exceed 60.7 kcal/mol. The 1,4-diradical decomposition enthalpies found as differences between 2 + 2 cycloreversion and ring-opening enthalpies were negative, the least exothermicity was calculated for , CH2SiH2CH2CH2. The only exception was 1,3-disiletane, which being diradical, CH2SiH2CH2SiH2, decomposed endothermically. Since decomposition of the diradical containing two silicon atoms required extra energy, raising the enthalpy of the overall reaction to 78.9 kcal/mol, 1,3-disiletane was predicted to be highly resisting to 2 + 2 cycloreversion. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:704,720, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20377 [source] Übergangsmetallkatalysierte direkte Arylierungen von (Hetero)Arenen durch C-H-BindungsbruchANGEWANDTE CHEMIE, Issue 52 2009Lutz Ackermann Prof. Abstract Das Gebiet der übergangsmetallkatalysierten direkten Arylierung unter C-H-Bindungsbruch hat in den letzten Jahren eine rasante Entwicklung erfahren, was dazu führte, dass sich solche Methoden immer mehr als Alternativen zu den herkömmlichen Kreuzkupplungen mit metallorganischen Reagentien etabliert haben. Insbesondere wurden zahlreiche Palladium- und Rutheniumkatalysatoren beschrieben, welche die direkte Arylierung von (Hetero)arenen mit anspruchsvollen Reaktionspartnern ermöglichen; hierzu gehören elektrophile Arylchloride und -tosylate oder auch einfache Arene in gekreuzten dehydrierenden Arylierungen. [source] Electrophilic Fluorocyclization of Allyl Silanes,ANGEWANDTE CHEMIE, Issue 38 2009Susan Frischen Wind in die Verwendung fluorierter Hetero- und Carbocyclen als Pharmaka und Agrochemikalien bringen allgemeine Fluorcyclisierungen. Bei Allylsilanen gelang nun die selektive Fluorierung-Cyclisierung mit N-F-Reagentien zu cis - und trans -substituierten fluorierten Heterocyclen (siehe Schema). Die Art der Silylgruppe entscheidet darüber, ob die konkurrierende Fluordesilylierung abläuft oder nicht. [source] Hetero- and homo-leptic Ru(II) catalyzed synthesis of cyclic carbonates from CO2; Synthesis, spectroscopic characterization and electrochemical propertiesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2010Ahmet Kilic Abstract Based on the a ligand BDPPZ [(9a,13a-dihydro-4,5,9,14-tetraaza-benzo[b]triphenylene-11-yl)-phenyl-methanone] (1) and its polypyridyl hetero- and homoleptic Ru(II) metal complexes, [Ru(bpy)2L](PF6)2 (2), [Ru(phen)2L](PF6)2 (3), [Ru(dafo)2L](PF6)2 (4), [Ru(dcbpy)2L](PF6)2 (5) and [RuL3](PF6)2 (6) (where, L = ligand, bpy = 2,2,-bipyridine, phen = 1,10-phenantroline, dafo = 4,5-diazafluoren-9-one and dcbpy = 3,3,-dicarboxy-2,2,-bipyridine), have been synthesized and characterized by elemental analysis, UV,vis, FT-IR, 1H and 13C-NMR spectra (for ligand), molar conductivity measurements and X-ray powder techniques. The electrochemical parameters of the substituted ligand and its polypyridyl hetero- and homoleptic Ru(II) metal complexes are reported by cyclic voltammetry. UV,vis spectroscopy is used to compare the differences between the conjugated , systems in this ligand and its Ru(II) metal complexes. The polypyridyl hetero- and homoleptic Ru(II) metal complexes also tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. The results showed that the [Ru(L)3](PF6)2 (6) complex is more efficient than the other Ru(II) complexes for the formation of cyclic organic carbonates from carbon dioxide. Copyright © 2010 John Wiley & Sons, Ltd. [source] ChemInform Abstract: Palladium-Catalyzed Direct Arylation-Based Domino Synthesis of Annulated N-Heterocycles Using Alkenyl or (Hetero)Aryl 1,2-Dihalides.CHEMINFORM, Issue 9 2010Lutz Ackermann 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] ChemInform Abstract: Selective Iridium-Catalyzed Alkylation of (Hetero)Aromatic Amines and Diamines with Alcohols under Mild Reaction Conditions.CHEMINFORM, Issue 32 2009Benoit Blank Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] ChemInform Abstract: A New Synthesis of 2-(Hetero)aryl-Substituted Pyrazines.CHEMINFORM, Issue 29 2009Arumugam Kodimuthali Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] ChemInform Abstract: Palladium-Catalyzed Direct (Hetero)arylation of Ethyl Oxazole-4-carboxylate: An Efficient Access to (Hetero)aryloxazoles.CHEMINFORM, Issue 5 2009Cecile Verrier Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] ChemInform Abstract: An Efficient Method for the Selective Iridium-Catalyzed Monoalkylation of (Hetero)aromatic Amines with Primary Alcohols.CHEMINFORM, Issue 32 2008Benoit Blank Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] ChemInform Abstract: A New Class of Substrates for Nucleophilic 5-endo-trig Cyclization, 2-Trifluoromethyl-1-alkenes: Synthesis of Five-Membered Hetero- and Carbocycles that Bear Fluorinated One-Carbon Units.CHEMINFORM, Issue 27 2008Junji Ichikawa Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] Synthesis of Hetero- and Carbocycles by Nucleophilic Substitution at sp2 Carbon.CHEMINFORM, Issue 41 2007Hironori Miyauchi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of Fused Imidazoles and Benzothiazoles from (Hetero)aromatic ortho-Diamines of ortho-Aminothiophenol and Aldehydes Promoted by Chlorotrimethylsilane.CHEMINFORM, Issue 12 2007Sergey V. Ryabukhin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A Simple Route to New Phenanthro- and Phenanthroid-Fused Thiazoles by a PIFA-Mediated (Hetero)biaryl Coupling Reaction.CHEMINFORM, Issue 43 2002Isabel Moreno Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: DBU, a Highly Efficient Reagent for the Facile Regeneration of (Hetero)arylamines from Their Acetamides and Benzamides: Influence of Solvent, Temperature, and Microwave Irradiation.CHEMINFORM, Issue 25 2002Manas Chakrabarty 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] Selective Iridium-Catalyzed Alkylation of (Hetero)Aromatic Amines and Diamines with Alcohols under Mild Reaction ConditionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Benoît Blank Abstract Selective amine alkylation: A P,N-ligand-stabilized iridium complex has been used as an efficient catalyst for the alkylation of (hetero)aromatic amines with alcohols at mild reaction temperatures and catalyst loadings as low as 0.1,mol,% Ir (see scheme). The excellent selectivity of the catalyst for monoalkylation of the amine function has also been exploited for the N,N,-dialkylation of diamines in both symmetric and nonsymmetric fashions. A P,N-ligand-coordinated iridium complex has been employed as an efficient catalyst for the selective monoalkylation of (hetero)aromatic amines with alcohols. A significant improvement of this alkylation method has been achieved, such that it can be performed at a temperature of 70,°C and with catalyst loadings as low as 0.1,mol,% Ir, while still affording excellent yields of secondary amines. Furthermore, the high selectivity of this catalyst for the monoalkylation of aromatic amino functions has been successfully exploited for the alkylation of diamines in both symmetric and nonsymmetric fashions, providing a novel and very efficient synthetic tool for the preparation of N,N,-dialkylated aromatic diamines. Ein P,N-Ligand-koordinierter Iridiumkomplex wird als ein effizienter Katalysator für die selektive Monoalkylierung von (hetero)aromatischen Aminen mit Alkoholen beschrieben. Eine signifikante Verbesserung dieser Alkylierungsmethode wurde erreicht. Bei Temperaturen von 70,°C und mit Katalysatorbeladungen von bis zu 0.1,mol,% Ir konnten exzellente Ausbeuten für sekundäre Amine erhalten werden. Weiterhin konnte die hohe Selektivität des Katalysators hinsichtlich der Monoalkylierung von aromatischen Aminogruppen genutzt werden, um Diamine symmetrisch und unsymmetrisch zu alkylieren. Damit steht ein neues sehr effizientes Synthesewerkzeug zur Darstellung von N,N, -alkylierten aromatischen Diaminen zur Verfügung. [source] Synthesis and Preferred All- syn Conformation of C3 -Symmetrical N -(Hetero)arylmethyl TriindolesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2008Abstract A new series of C3 -symmetrical N -(hetero)arylmethyl triindoles has been synthesized in a straightforward procedure. The structure and conformation in the solid state have been determined for three derivatives (3, 4, and 6) by X-ray crystallographic analysis. In all three cases, the molecules adopt a tripodal conformation with all of the flexible arms directed towards the same side, thereby delimiting an inner cavity. Compound 6 crystallizes and forms C3 -symmetric dimeric cagelike complexes. Guest molecules of chloroform and water are confined within the resulting cavities with stabilization by different intermolecular interactions; this highlights the potential of these compounds in the construction of supramolecular systems. A computational analysis has been performed to predict the most stable conformers. As a general trend, a preference for a conformation with all branches directed to the same side has been predicted. Comparison between theoretical and experimental results indicates that the computational level selected for the present study, B3LYP/6-31G*, is able to reproduce both the minimum energy conformations and the rotation barriers about the NCH2 bond. [source] Synthesis, Structure and Emission Properties of Spirocyclic Benzofuranones and Dihydroindolones: A Domino Insertion,Coupling,Isomerization, Diels,Alder Approach to Rigid FluorophoresCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2008Daniel Abstract An alkynoyl ortho -iodo phenolester or alkynoyl ortho -iodo anilides and propargyl allyl ethers react under Sonogashira coupling conditions in the sense of an insertion,coupling,isomerization,Diels,Alder hetero domino reaction to furnish (tetrahydroisobenzofuran)-spirobenzofuranones and -spirodihydroindolones in good yields. Many representatives can be crystallized and single crystal structure analyses display steric and electronic substituent effects on the torsional angles of the terminal (hetero)aryl groups and the central cis,trans -butadiene fragment. DFT computations reveal that in the final pericyclic step the Diels,Alder termination is by far thermodynamically and kinetically favored over a possible Claisen rearrangement. Compounds of this new class of spirocyclic compounds possess large Stokes shifts and fluoresce intensively with blue over green to orange colors. As a consequence of the spirocyclic rigidity fluorescence lifetimes and quantum yields are rather high in some cases. Alkinoyl ortho -iodphenolester oder Alkinoyl ortho -iodanilide und Propargylallylether reagieren unter den Bedingungen der Sonogashira-Kupplung im Sinne einer Insertions,Kupplungs,Diels,Alder-Hetero-Domino-Reaktion zu (Tetrahydroisobenzofuran)-spirobenzofuranonen bzw. -spirodihydroindolonen in guten Ausbeuten, von denen viele kristallisiert werden konnten. Die Einkristallstrukturanalysen offenbaren sterische und elektronische Substituenteneffekte auf die Torsionswinkel der terminalen (Hetero)arylgruppen und des zentralen cis,trans -Butadienfragments. DFT-Rechnungen zeigen, dass im letzten pericyclischen Schritt die Diels,Alder-Reaktion gegenüber einer möglichen Claisen-Umlagerung bei weitem thermodynamisch und kinetisch begünstigt ist. Viele Verbindungen dieser neuen Spirocyclenklasse besitzen große Stokes-Verschiebungen und fluoreszieren intensive mit blauer, grüner oder oranger Farbe. Als Folge der spirocyclischen Rigidität sind in einigen Fällen die Fluoreszenzlebensdauern und Quantenausbeuten relative hoch. [source] Solid-State Anion,Guest Encapsulation by Metallosupramolecular Capsules Made from Two Tetranuclear Copper(II) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2007Emilio Pardo Abstract A new cationic tetranuclear copper(II) complex self-assembles from one 1,3-phenylenebis(oxamato) (mpba) bridging ligand and four CuII ions partially blocked with N,N,N,,N, -tetramethylethylenediamine (tmen) terminal ligands. In the solid state, two of these tetracopper(II) oxamato complexes of bowl-like shape and helical conformation then serve as a building block for the generation of either hetero- (MP) or homochiral (MM/PP) dimeric capsules depending on the nature of the encapsulated anion guest, perchlorate or hexafluorophosphate. The overall magnetic behaviour of these metallosupramolecular capsules does not depend on the nature of the encapsulated anion guest, but it is consistent with the dimer-of-dimer structure of the tetracopper(II) cation host, where the interdimer magnetic coupling through the meta -phenylenediamidate bridge is negligibly smallrelative to the reasonably strong intradimer one across the oxamato bridge.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Biocatalytic Racemization of (Hetero)Aryl-aliphatic ,-Hydroxycarboxylic Acids by Lactobacillus spp.EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2006Proceeds via an Oxidation, Reduction Sequence Abstract The biocatalytic racemization of a range of (hetero)aryl- and (di)aryl-aliphatic ,-hydroxycarboxylic acids has been achieved by using whole resting cells of Lactobacillus spp. The essentially mild (physiological) reaction conditions ensure the suppression of undesired side reactions, such as elimination, decomposition or condensation. Cofactor/inhibitor studies using a cell-free extract of Lactobacillus paracasei DSM 20207 reveal that the addition of redox cofactors (NAD+/NADH) leads to a distinct increase in the racemization rate, while strong inhibition is observed in the presence of Thio-NAD+, which suggests that the racemization proceeds by an oxidation,reduction sequence rather than involvement of a "racemase" enzyme. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Generation of a Small Library of Highly Electron-Rich 2-(Hetero)Aryl-Substituted Phenethylamines by the Suzuki,Miyaura Reaction: A Short Synthesis of an Apogalanthamine AnalogueEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2004Prasad Appukkuttan Abstract The Suzuki,Miyaura reaction is presented as a versatile procedure for the synthesis of a small library of highly electron-rich 2-[4,5-dimethoxy-2-(hetero)arylphenyl]ethylamines. Microwave-irradiation accelerates the reaction tremendously and furnishes superior yields. The difficult oxidative addition of the catalyst to a highly electron-rich and ortho -substituted system could be performed easily, and the proto-deboronation during cross-coupling reactions involving the highly electron-withdrawing (2-formylphenyl)boronic acid could be minimized. Enhanced yields and complete compatibility with aqueous conditions were found. This strategy was developed en route towards the synthesis of an apogalanthamine analogue. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of Novel Polycyclic Indole-Annulated Thiopyranocoumarin Derivatives via Domino Knoevenagel,Hetero- Diels,Alder Reaction in Aqueous MediaHELVETICA CHIMICA ACTA, Issue 5 2010Firouz, Matloubi Moghaddam Abstract An efficient synthesis of polycyclic indole derivatives is achieved via domino Knoevenagel,hetero- Diels,Alder reaction of O -acrylated salicylaldehyde derivatives with dihydroindole-2-thiones in H2O as solvent. The products are formed in good-to-excellent yields with high regio- and stereoselectivity. [source] Reactivity and Selectivity of Captodative Olefins as Dienes in Hetero -Diels,Alder ReactionsHELVETICA CHIMICA ACTA, Issue 10 2008Rubén Sanabria Abstract The reactivity and selectivity of the the captodative olefins 1-acylvinyl benzoates 1a,1f and 3a as heterodienes in hetero -Diels,Alder reactions in the presence of electron-rich dienophiles is described. Heterodienes 1 undergo regioselective cycloaddition with the alkyl vinyl etherdienophiles 6a,b and 9 to give the corresponding dihydro-2H -pyrans 7, 8, and 10 under thermal conditions. The reactivity of these cycloadditions depends, to a large extent, on the electronic demand of the substituent in the aroyloxy group of the heterodiene. Frontier-molecular-orbital (FMO; ab initio) and density-functional-theory (DFT) calculations of the ground and transition states account for the reactivity and regioselectivity observed in these processes. [source] Synthesis of Components for the Generation of Constitutional Dynamic Analogues of Nucleic AcidsHELVETICA CHIMICA ACTA, Issue 1 2008David Abstract The introduction of dynamic covalent polymers, in which the monomer units are linked by reversible covalent bonds and can undergo component exchange, opens up new possibilities for the generation of functional materials. Extending this approach to the generation of dynamic biopolymers in aqueous media, which are able to adapt constitution (sequence, length) to external factors (e.g., environment, medium, template), would provide an alternative approach to the de novo design of functional dynamic bio-macromolecules. As a first step towards this goal, various mono- and bifunctionalised (hetero- and homotopic) nucleic acid-derived building blocks of type I,X have been synthesised for the generation of dynamic main-chain and side-chain reversible nucleic acid analogues. Hydrazide- and/or acetal (protected carbonyl)-functionalised components were selected, which differ in terms of flexibility, length, net formal charge, and hydrazide/acetal substituents, in order to explore how such factors may affect the properties (structure, solubility, molecular recognition features) of the polymer products that may be generated by polycondensation. [source] A Novel Coupling 1,3-Dipolar Cycloaddition Sequence as a Three-Component Approach to Highly Fluorescent IndolizinesHELVETICA CHIMICA ACTA, Issue 7 2005Alexandru Indolizines 4 and biindolizines 6 can be synthesized in moderate yields in a consecutive one-pot three-component process by a coupling/1,3-dipolar cycloaddition sequence of a (hetero)arenecarbonyl chloride 1, a terminal alkyne 2, and a suitable 1-(2-oxoethyl) pyridinium bromide 3 or 5, respectively (Schemes,1 and 2). After the Sonogashira coupling, a [2+3] cycloaddition of the in situ formed pyridinium ylide, an allyl-type 1,3-dipole, furnishes a cycloadduct that is instantaneously oxidatively aromatized to give the highly fluorescent indolizine derivatives that were unambiguously characterized by an X-ray-structure analysis of compound 4d (Fig.,1). Additionally, fluorescence studies with pyridinyl-substituted representatives reveal not only that indolizines and biindolizines are highly interesting fluorescence dyes but that their fluorescence color can also be reversibly switched upon altering the pH of the medium. [source] From mixed finite elements to finite volumes for elliptic PDEs in two and three dimensionsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2004Anis Younes Abstract The link between Mixed Finite Element (MFE) and Finite Volume (FV) methods applied to elliptic partial differential equations has been investigated by many authors. Recently, a FV formulation of the mixed approach has been developed. This approach was restricted to 2D problems with a scalar for the parameter used to calculate fluxes from the state variable gradient. This new approach is extended to 2D problems with a full parameter tensor and to 3D problems. The objective of this new formulation is to reduce the total number of unknowns while keeping the same accuracy. This is achieved by defining one new variable per element. For the 2D case with full parameter tensor, this new formulation exists for any kind of triangulation. It allows the reduction of the number of unknowns to the number of elements instead of the number of edges. No additional assumptions are required concerning the averaging of the parameter in hetero- geneous domains. For 3D problems, we demonstrate that the new formulation cannot exist for a general 3D tetrahedral discretization, unlike in the 2D problem. However, it does exist when the tetrahedrons are regular, or deduced from rectangular parallelepipeds, and allows reduction of the number of unknowns. Numerical experiments and comparisons between both formulations in 2D show the efficiency of the new formulation. Copyright © 2003 John Wiley & Sons, Ltd. [source] Novel Enantioselective Sequentially Rhodium(I)/BINAP- Catalyzed Cycloisomerization,Hydrogenation,Isomerization, Acetalization (CIHIA)ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Nadine Körber Abstract Linear, easily accessible alkyl and (hetero)aryl-substituted alkynyl allyl alcohols are readily and enantioselectively transformed into 2,7-dioxabicyclo[3.2.1]octanes by a sequential rhodium-catalyzed process. Based on the initial cycloisomerization, the in situ generated rhodium(I)-BINAP complex enables a subsequent reduction with hydrogen and the transformation into bicyclic frameworks. [source] | |||||||||||||||||||||||||||||||