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Catalyzed Reaction (catalyzed + reaction)
Selected AbstractsTheoretical Study on Hetero-Diels,Alder Reaction of Butadiene with Benzaldehyde Catalyzed by Chiral InIII ComplexesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2010Xiuli Cao Abstract The mechanism of the hetero-Diels,Alder reaction of butadiene with benzaldehyde catalyzed by chiral N,N, -dioxide/In(OTf)3 complexes was studied theoretically by using density functional theory (DFT) and model system. The computational results indicate that the catalyzed reaction proceeded through a concerted mechanism via a highly zwitterionic transition state. The lowest energy barrier was 11.8 kJ,mol,1, which is 63.0 kJ,mol,1 lower than that of the uncatalyzed reaction. The results indicate that the endo approach is advantageous over the exo approach, because exo transitions states suffer from more steric hindrance than the endo transitions states as a result of interactions among the substrates, the trifluoromethanesulfonic group and the R4 groups of the ligand. The (S) configuration was observed predominantly over the (R) form, because there is no distinguishable repulsion between butadiene and the exo amino side or the endo amino side of the ligand. Besides, the interactions between the terminal hydrogen atoms of butadiene and the oxygen atoms of the trifluoromethanesulfonic group make the structure more stable. Thus, the experimental results were explained well by calculation of the chiral N,N, -dioxide/In(OTf)3 complex catalyzed hetero-Diels,Alder reaction at the molecular level. [source] Directed evolution of formate dehydrogenase from Candida boidinii for improved stability during entrapment in polyacrylamideFEBS JOURNAL, Issue 17 2006Marion B. Ansorge-Schumacher In two cycles of an error-prone PCR process, variants of formate dehydrogenase from Candida boidinii were created which revealed an up to 4.4-fold (440%) higher residual activity after entrapment in polyacrylamide gels than the wild-type enzyme. These were identified in an assay using single precursor molecules of polyacrylamide instead of the complete gel for selection. The stabilization resulted from an exchange of distinct lysine, glutamic acid, and cysteine residues remote from the active site, which did not affect the kinetics of the catalyzed reaction. Thermal stability increased at the exchange of lysine and glutamic acid, but decreased due the exchange of cysteine. Overall, the variants reveal very suitable properties for application in a technical synthetic process, enabling use of entrapment in polyacrylamide as an economic and versatile immobilization method. [source] 6-(Diazomethyl)-1,3-bis(methoxymethyl)uracil, Synthesis and Transformation into Annulated PyrimidinedionesHELVETICA CHIMICA ACTA, Issue 7 2008Fuyi Zhang Abstract 6-(Diazomethyl)-1,3-bis(methoxymethyl)uracil (5) was prepared from the known aldehyde 3 by hydrazone formation and oxidation. Thermolysis of 5 and deprotection gave the pyrazolo[4,3- d]pyrimidine-5,7-diones 7a and 7b. Rh2(OAc)4 catalyzed the transformation of 5 into to a 2,:,1 (Z)/(E) mixture of 1,2-diuracilylethenes 9 (67%). Heating (Z)- 9 in 12n HCl at 95° led to electrocyclisation, oxidation, and deprotection to afford 73% of the pyrimido[5,4- f]quinazolinetetraone 12. The Rh2(OAc)4 -catalyzed reaction of 5 with 3,4-dihydro-2H -pyran and 2,3-dihydrofuran gave endo/exo -mixtures of the 2-oxabicyclo[4.1.0]heptane 13 (78%) and the 2-oxabicyclo[3.1.0]hexane 15 (86%), Their treatment with AlCl3 or Me2AlCl promoted a vinylcyclopropane,cyclopentene rearrangement, leading to the pyrano- and furanocyclopenta[1,2- d]pyrimidinediones 14 (88%) and 16 (51%), respectively. Similarly, the addition product of 5 to 2-methoxypropene was transformed into the 5-methylcyclopenta-pyrimidinedione 18 (55%). The Rh2(OAc)4 -catalyzed reaction of 5 with thiophene gave the exo -configured 2-thiabicyclo[3.1.0]hexane 19 (69%). The analoguous reaction with furan led to 8-oxabicyclo[3.2.1]oct-2-ene 20 (73%), and the reaction with (E)-2-styrylfuran yielded a diastereoisomeric mixture of hepta-1,4,6-trien-3-ones 21 (75%) that was transformed into the (1E,4E,6E)-configured hepta-1,4,6-trien-3-one 21 (60%) at ambient temperature. [source] The silver(I)-catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by phenylhydrazine in aqueous mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2007R. M. Naik The [Ag]+ -catalyzed exchange of coordinated cyanide in [Fe(CN)6]4, by phenylhydrazine (PhNHNH2) has been studied spectrophotometrically at 488 nm by monitoring increase in the absorbance for the formation of cherry red colored complex [Fe(CN)5PhNHNH2]3,. The other reaction conditions were pH 2.80±,0.02, temperature = 30.0 ± 0.1°C, and ionic strength (I) = 0.02 M (KNO3). The reaction was followed as a function of pH, ionic strength, temperature, [Fe(CN)4,6], [PhNHNH2], [Ag+] by varying one variable at a time. The initial rates were evaluated for each variation using the plane mirror method. The initial rates evaluated as a function of [Fe(CN)4,6] clearly indicate that the initial rate increases with the increase in [Fe(CN)4,6] and finally reaches to a limiting value when [Fe(CN)4,6]/[AgNO3] , 1000. It indicates the formation of a strong adduct between [Fe(CN)6]4, and AgNO3 prior to the abstraction of CN,. The variation in initial rates with [PhNHNH2] also showed limiting values at [Fe(CN)4,6]/[PhNHNH2] , 8.30. The complex behavior due to pH and [Ag+] variations on the rate has been explained in detail. The composition of the final reaction product [Fe(CN)5PhNHNH2] formed during the course of reaction has been found to be 1:1 using the mole ratio method. The evaluated values of activation parameters for the catalyzed reaction are Ea = 53.85 kJ mol,1, , H,, = 51.33 kJ mol,1, and , S, = ,134.63 J K,1 mol,1, which suggest an interchange dissociative mechanism. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 447,456, 2007 [source] Uncatalyzed and ruthenium(III)-catalyzed reaction of acidic chlorite with methylene violetINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2003S. B. Jonnalagadda The kinetics and mechanism of the uncatalyzed and Ru(III)-catalyzed oxidation of methylene violet (3-amino-7-diethylamino-5-phenyl phenazinium chloride) (MV+) by acidic chlorite is reported. With excess concentrations of other reactants, both uncatalyzed and catalyzed reactions had pseudo-first-order kinetics with respect to MV+. The uncatalyzed reaction had first-order dependence on chlorite and H+ concentrations, but the catalyzed reaction had first-order dependence on both chlorite and catalyst, and a fractional order with respect to [H+]. The rate coefficient of the uncatalyzed reaction is (5.72 ± 0.19) M,2 s,1, while the catalytic constant for the catalyzed reaction is (22.4 ± 0.3) × 103 M,1 s,1. The basic stoichiometric equation is as follows: 2MV+ + 7ClO2, + 2H+ = 2P + CH3COOH + 4ClO2 + 3Cl,, where P+ = 3-amino-7-ethylamino-5-phenyl phenazinium-10-N-oxide. Stoichiometry is dependent on the initial concentration of chlorite present. Consistent with the experimental results, pertinent mechanisms are proposed. The proposed 15-step mechanism is simulated using literature; experimental and estimated rate coefficients and the simulated plots agreed well with the experimental curves. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 294,303, 2003 [source] A Dramatic Substituent Effect in Silver(I)-Catalyzed Regioselective Cyclization of ortho -Alkynylaryl Aldehyde Oxime DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Hongyin Gao Abstract A dramatic substituent effect was found in the silver(I)-catalyzed cyclization reaction of ortho -alkynylaryl aldehyde oxime derivatives. When R is an alkyl group, the Ag(I)-catalyzed reaction in dimethylacetamide at 110,°C (conditions A) affords isoquinolines in good to excellent yields, in contrast, isoquinolin-1(2,H)-ones were produced in moderate to high yields under conditions B (dimethylformamide, room temperature) when R is an acetyl group. A plausible mechanism was proposed for this product selectivity control reaction (PSCR) by subtle structure modification. [source] Unexpected regioselectivity in the palladium-catalyzed reaction of silacyclobutanes with aryl iodidesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2001Yoshifumi Tanaka Abstract The reaction of aryl iodides with 1,1-diphenyl-silacyclobutane in the presence of a catalytic amount of Pd(PPh3)4 affords unexpected ring-opening adducts, 1- and 2-propenyl(triaryl)-silanes, in good yields. On the other hand, the PdCl2(PhCN)2 -catalyzed reaction of 1,1-diphenylsilacyclobutanes with aryl halides gives unexpected products, triarylsilanols, after hydrolysis in moderate yields. The catalysis involves the reaction of aryl,palladium intermediates with silacyclobutanes along with regioselective aryl,silicon bond formation. Copyright © 2001 John Wiley & Sons, Ltd. [source] Lipoprotein Mutation Accelerates Substrate Permeability-Limited Toluene Dioxygenase-Catalyzed ReactionBIOTECHNOLOGY PROGRESS, Issue 3 2005Ye Ni One of the major problems in whole-cell biocatalysis is its low reaction rate. The underlying cause is the substrate permeation barrier presented by cell envelopes. The present research investigates mutation effects of the Braunapos;s lipoprotein, the most abundant outer membrane structural protein in Escherichia coli, on toluene dioxyengase (TDO)-catalyzed reaction. Dramatic enhancement of the reaction rate, an increase of up to 6-fold, was observed with the mutant for all three small, hydrophobic substrates tested (toluene, ethylbenzene, and 2-indanone). The increase was observed over a wide range of substrate concentrations (0.1,5 mM). The mutant exhibited a normal growth rate and expressed the recombinant multicomponent enzyme as well as the isogenic parent strain. Taken together, the lipoprotein mutant expressing TDO is a much better whole-cell catalyst for the oxidation reaction. The beneficial effect of the lipoprotein mutation may be general for a broad range of substrates and enzyme systems as the mutation affects the global integrity of the cell membrane. A comparison of the mutation effect with a common permeabilizing procedure, the EDTA treatment, further illustrates the clear advantages of using genetic modification in cellular membrane engineering for improved whole-cell catalysts. [source] Neutral Group-IV Metal Catalysts for the Intramolecular Hydroamination of AlkenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2008Carsten Müller Abstract A detailed comparison of the group-IV metal catalysts Ti(NMe2)4, Ind2TiMe2, Ind2ZrMe2 and Ind2HfMe2 in the intramolecular hydroamination of amino alkenes is presented. Among these catalysts, the benchmark catalyst Ti(NMe2)4 is the most active in the formation of pyrrolidines. A comparison between Ind2TiMe2, Ind2ZrMe2 and Ind2HfMe2 suggests that in the synthesis of pyrrolidines, Zr complexes show the highest catalytic activity of the group-IV metal catalysts. Although Ind2TiMe2 - and the Ind2ZrMe2 -catalyzed formation of a pyrrolidine is first-order in the concentration of the substrate, the corresponding Ti(NMe2)4 -catalyzed cyclization is second-order in the concentration of the substrate. The results obtained for the formation of piperidines catalyzed by Ti(NMe2)4, Ind2TiMe2, Ind2ZrMe2 and Ind2HfMe2 suggest that for these reactions, Ti catalysts show increased catalytic activity compared with the corresponding Zr catalysts. Unfortunately, the formation of aminocyclopentane side-products by C,H activation processes is a severe drawback of the Ti catalysts. The corresponding side-products are not formed in Ind2ZrMe2 - and Ind2HfMe2 -catalyzed reactions. However, the former catalyst gives better yields of the desired piperidine products. In contrast to the results obtained for the synthesis of pyrrolidines, the formation of a piperidine is zero-order in the concentration of the substrate for the indenyl catalysts Ind2TiMe2 and Ind2ZrMe2, and first-order for the homoleptic catalyst Ti(NMe2)4. Interestingly, Ind2TiMe2 is able to catalyze a slow hydroamination of an N -methylated amino alkene, whereas the homoleptic complex Ti(NMe2)4 as well as Ind2ZrMe2 and Ind2HfMe2 do not catalyze the same reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] The Synthesis of Polysubstituted Pyrroles via the Coupling of Phenyliodonium Ylides and Enamine EstersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Jun-Yan Wang Abstract The boron trifluoride etherate (BF3,Et2O)-catalyzed reactions between phenyliodonium ylides and enamine esters provide an efficient method for the synthesis of polysubstituted pyrroles. [source] Quantitative structure,reactivity relationship studies on the catalyzed Michael addition reactionsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2009Bahram Hemmateenejad Abstract Quantitative structure,reactivity relationship (QSRR) can be considered as a variant of quantitative structure,property relationship (QSPR) studies, where the chemical reactivity of reactants or catalysts in a specified chemical reaction is related to chemical structure. In this manner, the Michael addition of some different substrates using different catalysts (SDS, silica gel, and ZrOCl2) was subjected to structure,reactivity relationship, quantitatively. Multiple linear regression (MLR) and partial least square (PLS) were used to perform the QSRR analysis. The resulted models for different catalyzed reactions showed that the catalysts probably act in different mechanisms since the models obtained for the catalysts included different parameters from substrate and enones. Overall, it was found that the reactivity in Michael addition reactions is controlled by coulombic (dipole and charge) interactions as well as the orbital energetic parameters. In the presence of different catalysts, the relative importance of these parameters is changed and hence the catalytic activity is changed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Gold(I)-Catalyzed Intermolecular Hydroarylation of Alkenes with Indoles under Thermal and Microwave-Assisted ConditionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2008Ming-Zhong Wang Abstract An efficient method for intermolecular hydroarylation of aryl and aliphatic alkenes with indoles using a combination of [(PR3)AuCl]/AgOTf as catalyst under thermal and microwave-assisted conditions has been developed. The gold(I)-catalyzed reactions of indoles with aryl alkenes were achieved in toluene at 85,°C over a reaction time of 1,3,h with 2,mol,% of [(PR3)AuCl]/AgOTf as catalyst. This method works for a variety of styrenes bearing electron-deficient, electron-rich, and sterically bulky substituents to give the corresponding products in good to high yields (60,95,%). Under microwave irradiation, coupling of unactivated aliphatic alkenes with indoles gave the corresponding adducts in up to 90,% yield. Selective hydroarylation of terminal CC bond of conjugated dienes with indoles gave good product yields (62,81,%). On the basis of deuterium-labeling experiments, a reaction mechanism involving nucleophilic attack of Au(I)-coordinated alkenes by indoles is proposed. [source] Luminescent Excited-State Intramolecular Proton-Transfer (ESIPT) Dyes Based on 4-Alkyne-Functionalized [2,2,-Bipyridine]-3,3,-diol DyesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2008Gilles Ulrich Dr. Abstract Functionalized 6,6,-dimethyl-3,3,-dihydroxy-2,2,-bipyridine dyes (BP(OH)2) exhibit relatively intense fluorescence from the relaxed excited state formed by excited-state intramolecular proton transfer (ESIPT). Bromo functionalization of (BP(OH)2) species followed by palladium(0)-catalyzed reactions allows the connection (via alkyne tethers) of functional groups, such as the singlet-emitter diazaboraindacene (bodipy) group or a chelating module (terpyridine; terpy). The X-ray structure of the terpy-based compound confirms the planarity of the 3,3,-dihydroxy-bipyridine unit. The new dyes exhibit relatively intense emission on the nanosecond timescale when in fluid solution, in the solid state at 298,K, and in rigid glasses at 77,K. In some cases, the excitation wavelength luminescence was observed and attributed to 1),inefficiency of the ESIPT process in particular compounds when not enough vibrational energy is introduced in the Franck,Condon state, which is populated by direct light excitation or 2),the presence of an additional excited state that deactivates to the ground state without undergoing the ESIPT process. For some selected species, the effect of the addition of zinc salts on the absorption and luminescence spectra was investigated. In particular, significant fluorescence changes were observed as a consequence of probable consecutive formation of a 1:1 and 1:2 molecular ratio of ligand/zinc adducts owing to coordination of ZnII ions by the bipyridyldiol moieties, except when an additional terpyridine subunit is present. In fact, this latter species preferentially coordinates to the ZnII ion in a 1:1 molecular ratio and further inhibits ZnII interaction. In the hybrid Bodipy/BP(OH)2 species, complete energy transfer from the BP(OH)2 to the bodipy fluorophore occurs, leading to exclusive emission from the lowest-lying bodipy subunit. Des composés colorés à base de 6,6,-dimethyl-3,3,-dihydroxy-2,2,-bipyridine (BP(OH)2) ont été synthétisés et présentent une fluorescence relativement intense issue de la relaxation d,un état excité provenant d,un transfert de proton dans l,état excité (ESIPT). La bromation de dérivés (BP(OH)2) suivie d,un couplage croisé catalysé par du Pd0sous-ligandé permet de connecter (par l,intermédiaire de pont alcyne) des groupes fonctionnels comme un groupe émetteur singulet de type boradiazaindacène (Bodipy) ou un module chélatant universel (une terpyridine). Une structure par diffraction aux rayons X a été obtenu avec le dérivé terpyridine, celle ci confirme la planéité de l,unité 3,3,-dihydroxy-bipyridine. Les nouveaux fluorophores possèdent une émission relativement intense avec une durée de vie de l,ordre de la nanoseconde, en solution et à l,état solide à 298,K ainsi que dans un verre à 77,K. Dans certain cas, la luminescence dépend de la longueur d,onde d,excitation, ce phénomène est attribué à (i) l,inefficacité du processus ESIPT, quand trop peu d,énergie vibrationnelle est introduite dans l,état Franck-Condon peuplé directement par la lumière d,excitation (ii) la présence d,un état excité supplémentaire qui désactive l,état fondamental sans passer par un processus ESIPT. Pour certains composés, l,effet de l,addition de sels de Zinc sur les spectres d,absorption et d,émission a été étudié : en particulier, des changements significatifs de fluorescence ont été observés, probablement due à la formation consécutive de complexes ligand/zinc de st,chiométrie 1:1 et 1:2, provenant de la coordination des cations ZnIIpar l,unité bipyridyl-diol, sauf quand une fonction terpyridine est présente. En fait, dans cette dernière espèce le zinc est préférentiellement coordiné par la terpyridine dans un ratio 1:1, et toute coordination supplémentaire de Zinc semble inhibée. Dans le composé hybride Bodipy/BP(OH)2,un transfert d,énergie quantitatif est observé du BP(OH)2vers le fluorophore Bodipy, entraînant une émission exclusive de la sous-unité Bodipy. Composti basati sulla subunità 6,6,-dimetil-3,3,-dididrossi-2,2,-bipiridina (BP(OH)2), variamente funzionalizzati, presentano fluorescenza relativamente intensa da stati eccitati formati attraverso trasferimento protonico nello stato eccitato (ESIPT). Bromo-funzionalizzazione dei composti di tipo BP(OH)2, seguita da reazioni catalizzate da Pd(0), permettono di connettere (con legame alchinico) gruppi funzionali quali il diazaboroindacene (Bodipy) o un modulo chelante (terpiridina) al frammento BP(OH)2. La struttura ai raggi X del composto contenente la terpiridina conferma la planarità dell,unità 3,3,-diidrossi-bipiridina. Le nuove specie presentano intensa emissione nella scala dei nanosecondi, in soluzione fluida ed allo stato solido a 298,K ed in matrice rigida a 77,K. In alcuni casi, la luminescenza dipende dalla lunghezza d,onda di eccitazione: questo fenomeno è attribuito a (i) inefficienza del processo ESIPT, quando non sufficiente energia vibrazionale è introdotta nello stato Franck-Condon a seguito di eccitazione luminosa o (ii) alla presenza di uno stato eccitato addizionale che si disattiva allo stato fondamentale senza passare dallo stato eccitato prodotto attraverso il meccanismo ESIPT. Per composti selezionati è stato anche studiato l,effetto della presenza di sali di zinco sulle proprietà di assorbimento elettronico e di luminescenza: significativi cambiamenti della fluorescenza sono stati osservati, come conseguenza della consecutiva formazione di addotti 1:1 e 1:2 (rapporto molare BP(OH)2/zinco), dovuta alla coordinazione di cationi di ZnIIda parte del bipiridil-diolo, che si verifica in tutti i casi studiati tranne in presenza di una subunità terpiridinica. In quest,ultimo caso, infatti, si forma soltanto l,addotto 1:1, e ulteriore coordinazione di cationi di ZnIIappare inibita. Nella specie ibrida Bodipy/BP(OH)2si verifica un completo trasferimento di energia elettronica dal BP(OH)2 al Bodipy, che porta ad emissione esclusivamente dalla subunità Bodipy, a piû bassa energia. [source] | ||||||||||||||||||||||