C Coupling (c + coupling)

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Chemistry80%

Terms modified by C Coupling

  • c coupling reaction
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    Selected Abstracts

    Three Phase Microemulsion/Sol,Gel System for Aqueous C,C Coupling of Hydrophobic Substrates

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2008
    Dmitry Tsvelikhovsky
    Abstract Heck, Stille, Suzuki and three-component coupling reactions with hydrophobic substrates have been carried out in water. The substrates are initially transformed by a general procedure into a microemulsion, which consists of nearly 90,% water with the aid of sodium dodecyl sulfate and either PrOH or BuOH. The surfactant carries the molecules of the substrates to Pd(OAc)2 entrapped within a hydrophobicitized silica sol,gel matrix where the coupling between the substrates is assumed to take place. The products are then returned by the surfactant into the microemulsion from which it can be released. The immobilized palladium catalyst is leach proof and recyclable. It can be used in various coupling processes at least six times without loss of activity. Experiments with D2O have revealed that the water does not take part in the coupling process, but it has an effect on the pore size of the sol,gel matrix, which hosts the palladium catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    ,-Hydroxy Esters via Enantioselective Hydrogen-Mediated C,C Coupling: Regiocontrolled Reactions of Silyl-Substituted 1,3-Diynes.

    CHEMINFORM, Issue 51 2006
    Chang-Woo Cho
    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]

    The effect of number of lengthening contractions on rat isometric force production at different frequencies of nerve stimulation

    ACTA PHYSIOLOGICA, Issue 3 2009
    M. E. T. Willems
    Abstract Aim:, To test the effect of 3, 10, 60 and 240 lengthening contractions (LC) on maximal isometric force of rat plantar flexor muscles at different stimulation frequencies. Methods:, Using a dynamometer and electrical nerve stimulation, maximally active skeletal muscles were stretched by ankle rotation to produce LC of the plantar flexor muscles in intact female rats. After the lengthening contraction protocols, maximal isometric force was measured at different frequencies of nerve activation to obtain frequency-dependent force deficits (weakness). Results:, The magnitude of the force deficit, measured 1 h after the protocols at 80 Hz, increased as a function of repetition number (three LC, 33.3 ± 1.7%; 10 LC, 37.2 ± 2.3%; 60 LC, 67.6 ± 1.5%; 240 LC, 77.7 ± 1.2%). Force deficits were also measured at each stimulation frequency tested (5:120 Hz). Using a ratio of isometric force at 20:100 Hz stimulation, the relative depression of force at low frequency was determined. The relative depression of isometric force at low frequency was most prominent during the early repetitions. Conclusion:, As low-frequency force depression appears to result primarily from excitation,contraction (E,C) coupling failure, the early LC in a series of repeated contractions probably contribute most to damage of the cellular components involved in E,C coupling. [source]

    Mono-, Bi- and Tridentate N-Heterocyclic Carbene Ligands for the Preparation of Transition-Metal-Based Homogeneous Catalysts

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2009
    Rosa Corberán
    Abstract This microreview focuses on the preparation of homogeneous catalysts of group 8,11 metals containing N-heterocyclic carbene ligands. The current status of the design of mono-, bi- and tridentate NHC ligands is reviewed through the description of the authors' own work. The catalytic applications of such complexes include hydrogen-borrowing, C,C coupling, reduction of double bonds and C,H activation reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Synthesis of Hafnacyclopentanes from Hafnocene Alkyne Complexes: Influence of Styrene Substituents on the C,C Coupling Regioselectivity

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2009
    Torsten Beweries
    Abstract The alkyne complex rac -(ebthi)Hf(,2 -Me3SiC2SiMe3) (1)[ebthi = 1,2-ethylene-1,1,-bis(,5 -tetrahydroindenyl)] reacts with styrene and p -(trifluoromethyl)styrene to give hafnacyclopentanes 2 and 3, respectively. C,C coupling proceeds in different ways: whereas for complex 2 a hafnacyclopentane with substituents in the ,,,-position is formed, in the latter case only ,,, coupling was observed. Complexes 2 and 3 can be activated with B(C6F5)3 to form active catalysts for the polymerization of ethylene.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    "Inhibition" of the Enzyme Model TpPh,MeZn,OH by Diketo Compounds

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2006
    Teame Tekeste
    Abstract In order to gain a structural understanding of zinc enzyme inhibition, the model complex TpPh,MeZn,OH was treated with various diketo compounds. ,-Keto carboxylic acids were attached to the zinc ion as anionic O,O-chelate ligands, of which benzoylformate was oxidatively decarboxylated in air to form the benzoate complex. Two functionalized ,-diketones did not use their functionality in forming the ,-diketonate complexes. Of the ,-diketones, 2,3-pentanedione formed the ,-keto enolate complex, while 1-phenyl-1,2-propanedione underwent oxidative C,C coupling resulting in a red dinuclear bis(,-keto enolato) complex. Of the diaryl-,-diketones, benzil did not react, but pyridil underwent hydrolytic cleavage to pyridine-2-carbaldehyde and picolinate, of which the latter was bound to the zinc ion as an N,O-chelate ligand.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Very Fast Suzuki,Miyaura Reaction Catalyzed by Pd(OAc)2 under Aerobic Conditions at Room Temperature in EGME/H2O

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2009
    Alessandro Del Zotto
    Abstract The results of a ligand-free Pd(OAc)2 -catalyzed Suzuki,Miyaura C,C coupling performed at room temperature under aerobic conditions are presented. It was found that the use of an ethylene glycol monomethyl ether/H2O mixture as the solvent resulted in very rapid reactions of aryl bromides with arylboronic acids. As a matter of fact, under optimized conditions, some substrates were converted quantitatively in less than 1 min with exceptionally high TOF values. For example, the reaction between 4-methoxyphenylboronic acid and bromobenzene afforded 4-methoxybiphenyl in 30 s with TOF = 180000 h,1. Furthermore, the reaction tolerates a wide range of functional groups and can be successfully applied to heteroaryl bromides such as 2-bromopyridine and 5-bromopyrimidine. Interestingly, also an activated aryl chloride such as 1-chloro-4-nitrobenzene reacted quantitatively with phenylboronic acid at 373 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    The Mechanism of the Stetter Reaction , A DFT Study

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2008
    Kirsty J. Hawkes
    Abstract On the basis of Breslow's mechanism for benzoin condensation, a model asymmetric Stetter reaction has been investigated using DFT methods. In contrast to the concerted benzoin condensation, after formation of the Breslow intermediate the Stetter reaction is found to be a two-step process in which the rate-determining C,C coupling of the Breslow intermediate and the Michael acceptor precedes final proton transfer. In addition, the enolamine is found to play a significant role in the stereochemistry of the product, with the energy difference between stereoisomers of this intermediate reflected throughout the remainder of the reaction sequence. Consequently, electronic and steric control of the stereochemistry of this intermediate should directly enhance the ee values of the product. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Chiral iridium(I) bis(NHC) complexes as catalysts for asymmetric transfer hydrogenation

    APPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2010
    Claus Diez
    Abstract The common use of NHC complexes in transition-metal mediated C,C coupling and metathesis reactions in recent decades has established N -heterocyclic carbenes as a new class of ligand for catalysis. The field of asymmetric catalysis with complexes bearing NHC-containing chiral ligands is dominated by mixed carbene/oxazoline or carbene/phosphane chelating ligands. In contrast, applications of complexes with chiral, chelating bis(NHC) ligands are rare. In the present work new chiral iridium(I) bis(NHC) complexes and their application in the asymmetric transfer hydrogenation of ketones are described. A series of chiral bis(azolium) salts have been prepared following a synthetic pathway, starting from L -valinol and the modular buildup allows the structural variation of the ligand precursors. The iridium complexes were formed via a one-pot transmetallation procedure. The prepared complexes were applied as catalysts in the asymmetric transfer hydrogenation of various prochiral ketones, affording the corresponding chiral alcohols in high yields and moderate to good enantioselectivities of up to 68%. The enantioselectivities of the catalysts were strongly affected by the various, terminal N -substituents of the chelating bis(NHC) ligands. The results presented in this work indicate the potential of bis-carbenes as stereodirecting ligands for asymmetric catalysis and are offering a base for further developments. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Effects of chlorpromazine on excitation,contraction coupling events in fast-twitch skeletal muscle fibres of the rat

    BRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2004
    R Wagner
    Single mechanically skinned fibres from the rat extensor digitorum longus muscle, which allow access to intracellular compartments, were used to examine the effects of 0.5,100 ,M chlorpromazine hydrochloride (CPZ) on the major steps of the excitation,contraction (E,C) coupling to elucidate the involvement of skeletal muscle in the neuroleptic malignant syndrome (NMS). At 1 ,M, CPZ caused a 20,30% increase in the force response induced by t-system depolarisation and a marked increase in the rate of caffeine-induced SR Ca2+ release. At [CPZ]2.5 ,M, there was an initial increase followed by a marked decrease of the t-system depolarisation-induced force responses, while the potentiating effect on the caffeine-induced SR Ca2+ release remained. These effects were reversible. CPZ had no effect on the maximum Ca2+ -activated force, but caused reversible, concentration-dependent increases in the Ca2+ sensitivity of the contractile apparatus at [CPZ] 10 ,M, with a 50% predicted shift of 0.11 pCa (,log [Ca2+]) units at 82.3 ,M CPZ. CPZ did not alter the rate of SR-Ca2+ loading at 1 and 10 ,M, but reversibly reduced it by ,40% at 100 ,M by reducing the SR Ca2+ pump. Nevertheless, the SR Ca2+ content was greater when fibres became unresponsive to t-system-induced depolarisation in the presence than in the absence of 100 ,M CPZ. The results show that CPZ has concentration-dependent stimulatory and inhibitory effects on various steps of the E,C coupling, which can explain the involvement of skeletal muscle in NMS and reconcile previous divergent data on CPZ effects on muscle. British Journal of Pharmacology (2004) 141, 624,633. doi:10.1038/sj.bjp.0705655 [source]