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Coupling Strategy (coupling + strategy)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Synthesis of Heteroarylazulenes: Transition Metal Free Coupling Strategy of Azulene with Heterocycles.

CHEMINFORM, Issue 20 2007
Taku Shoji
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]

Green Protocol for Annulation of the s-Triazine Ring on Thiazoles Using a Three-Component Coupling Strategy.

CHEMINFORM, Issue 39 2006
Lal Dhar S. Yadav
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]

Enantioselective Total Synthesis of Brevetoxin A: Convergent Coupling Strategy and Completion

CHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2009
Michael
Abstract A highly convergent, enantioselective total synthesis of brevetoxin A is reported. The development of a [X+2+X] Horner,Wadsworth,Emmons/cyclodehydration/reductive etherification convergent coupling strategy allowed a unified approach to the synthesis of two advanced tetracyclic fragments from four cyclic ether subunits. The Horner,Wittig coupling of the two tetracyclic fragments provided substrates that were explored for reductive etherification, the success of which delivered a late-stage tetraol intermediate. The tetraol was converted to the natural product through an expeditious selective oxidative process followed by methylenation. [source]

On the use of anisotropic a posteriori error estimators for the adaptative solution of 3D inviscid compressible flows

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2009
Y. Bourgault
Abstract This paper describes the use of an a posteriori error estimator to control anisotropic mesh adaptation for computing inviscid compressible flows. The a posteriori error estimator and the coupling strategy with an anisotropic remesher are first introduced. The mesh adaptation is controlled by a single-parameter tolerance (TOL) in regions where the solution is regular, whereas a condition on the minimal element size hmin is enforced across solution discontinuities. This hmin condition is justified on the basis of an asymptotic analysis. The efficiency of the approach is tested with a supersonic flow over an aircraft. The evolution of a mesh adaptation/flow solution loop is shown, together with the influence of the parameters TOL and hmin. We verify numerically that the effect of varying hmin is concordant with the conclusions of the asymptotic analysis, giving hints on the selection of hmin with respect to TOL. Finally, we check that the results obtained with the a posteriori error estimator are at least as accurate as those obtained with anisotropic a priori error estimators. All the results presented can be obtained using a standard desktop computer, showing the efficiency of these adaptative methods. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Pyrazole Synthesis Using a Titanium-Catalyzed Multicomponent Coupling Reaction and Synthesis of Withasomnine

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009
Supriyo Majumder
Abstract The titanium-catalyzed 3-component coupling of an alkyne, isonitrile, and amine can be used to generate tautomers of 1,3-diimines. These diimines produced in situ undergo cyclization with hydrazine and hydrazine derivatives in a one-pot procedure to provide pyrazoles. Seventeen examples of pyrazoles are provided using this one-pot, 4-component procedure from simple starting materials. The regioselectivity of the alkyne addition can be controlled in some cases with catalyst architecture, and regioselectivity of monosubsituted hydrazines to unsymmetrical 1,3-diimines is discussed. This multicomponent coupling strategy was applied to the synthesis of withasomnine in an efficient procedure, which gave the natural product in 24% overall yield from 4-pentyn-1-ol. [source]

Synthesis of tritium labelled delta sleep-inducing peptide

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 7 2001
Matthieu Giraud
Abstract The ,,, -dehydro precursor of the delta sleep-inducing peptide (DSIP) for tritiation was prepared prior to tritiation using a 3+6 fragment coupling strategy on a solid support. The first fragment, ,,, -dehydrotripeptide, was prepared in solution in five steps in 79% overall yield while the second fragment was obtained by a step by step peptide synthesis on a Wang resin using an Fmoc strategy. The ,,, -dehydrotripeptide was coupled to the fragment linked to the resin, followed by a deprotection/cleavage step to yield the ,,, -dehydro-DSIP, 7. Catalytic reduction of unsaturated DSIP using tritium gas and palladium oxide as catalyst gave [3H]DSIP having a specific activity of 1.184 TBq/mmol(32 Ci/mmol). Copyright © 2001 John Wiley & Sons, Ltd. [source]

A "Click" Strategy for Tuning in situ the Hydrophilic,Hydrophobic Balance of AB Macrosurfactants

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 12-13 2008
Zoya Zarafshani
Abstract The self-organization of amphiphilic block copolymers in water strongly depends on their molecular structure, in particular on their hydrophilic,hydrophobic balance. Herein, a simple method for tuning the amphiphilicity of polymeric macrosurfactants in aqueous medium is proposed. This concept relies on the "click" ligation of an amphiphilic block copolymer (AB type) and a hydrophilic homopolymer (B type). In the present communication, the validity of this approach was examined with model polymers based on polystyrene (PS) and poly[oligo (ethylene glycol) acrylate] (POEGA) segments. A well-defined , -azido functional diblock copolymer PS- b -POEGA and an , -alkyne functional homopolymer POEGA were prepared using atom transfer radical polymerization. These two polymers could be efficiently coupled to each other via copper-catalyzed azide,alkyne click chemistry in aqueous medium. Moreover, in this coupling strategy, an ester group was introduced at the junction between AB and B segments. This labile moiety may be "cut" by hydrolysis. [source]

Challenges of introducing quantitative elementary reactions in multiscale models of thin film deposition

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2010
Alessandro Barbato
Abstract The implementation of detailed surface kinetic mechanisms describing the thin film growth dynamics into models of chemical vapor deposition (CVD) reactors has been a challenge for many years. In this article we review the literature concerning the study of the dynamics of the Si(100)2,×,1 surface and introduce a multiscale model that captures the main features of its reactivity. The model combines the results of ab initio calculations with an atomistic description of the Si surface, obtained using a 3D-kinetic Monte Carlo (KMC) model that explicitly accounts for the 2,×,1 surface reconstruction and the formation and diffusion of Si dimers on a hydrogenated surface. At the atomistic scale, we determined pre-exponential factors and activation energies of hydrogen desorption reactions proceeding through the 2H, 3H, and 4H mechanisms. The calculated kinetic constants were embedded in the KMC model and used to simulate literature TPD experimental data. The simulations were used to fit the activation energies of hydrogen desorption reactions, which showed that DFT calculations performed with B3LYP functionals are likely to overestimate hydrogen desorption energies by up to 9,kcal,mol,1, which was confirmed by successive ab initio calculations. Two examples of the solution of the KMC model in conjunction with a reactor scale model are provided, in which the coupling was performed adopting both a hierarchic and a two-way coupling strategy. We found that in the plasma deposition of nanocrystalline silicon performed at low substrate temperatures the growth proceeds through a layer-by-layer mechanism on a surface almost completely covered by hydrogen. The application of the same model to the simulation of the thermal CVD of Si showed that at intermediate growth temperatures, when the hydrogen surface concentration is high, a new hydrogen desorption mechanism, in which Si adatoms play an important role, is active. Length scales encountered in multiscale modeling of thin films deposition. [source]

Some numerical properties of approaches to physics,dynamics coupling for NWP

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 614 2006
Mark Dubal
Abstract At the present time there exist a number of different approaches to the problem of coupling parametrized physical processes to the dynamical core in operational numerical weather-prediction (NWP) and climate models. Motivated by the various strategies in use, some idealized representative coupling schemes are constructed and subsequently analysed using a methodology in which the physics and dynamics terms are represented in a simplified way. Particular numerical properties of the idealized schemes which are of interest are the ability to capture correct steady-state solutions and to be second-order accurate in time. In general, the schemes require specific choices for the time-differencing of certain coupled processes if correct steady-state solutions are to be obtained. This has implications for the overall numerical stability of a coupling strategy. An alternative physics,dynamics coupling approach is then described and analysed. A multiple-sweep predictor,corrector coupling scheme is shown to capture the correct steady-state solution and to allow for second-order accuracy, provided that the convective process is coupled explicitly. This approach has a number of advantages over those currently used in operational NWP models. Copyright © 2006 Crown copyright [source]