bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Efficient Domino Approach for the Synthesis of Multisubstituted Pyrroles via Gold/Silver‐Catalyzed Amination/Cycloisomerization of (Z)‐2‐En‐4‐yn‐1‐ols
Authors: Lu Yuhua , Fu Xiaoping , Chen Haoyi , Du Xiangwei , Jia Xueshun , Liu Yuanhong 
Published: December 2008

AbstractAn efficient and one‐pot synthesis of multisubstituted pyrroles with high diversity and in a regioselective manner from the reactions of suitably substituted (Z)‐enynols with amines or sulfonamides under mild reaction conditions has been developed. This synthesis was realized via a cascade process in the presence of gold/silver (Au/Ag) or boron trifluoride⋅etherate/gold/silver (BF3⋅Et2O/Au/Ag) catalysts, which could catalyze amination and cycloisomerization reactions in the same vessel.
TEMPO‐tert‐Butyl Nitrite: An Efficient Catalytic System for Aerobic Oxidation of Alcohols
Authors: He Xijun , Shen Zhenlu , Mo Weimin , Sun Nan , Hu Baoxiang , Hu Xinquan 
Published: December 2008

AbstractA metal‐free catalytic system consisting of 2,2,6,6‐tetramethylpiperidineN‐oxyl (TEMPO) andtert‐butyl nitrite has been developed to activate molecular oxygen for the aerobic oxidation of alcohols. A variety of active and non‐active alcohols were oxidized to their corresponding carbonyl compounds in high selectivity and yields.
Reduction of Alkyl Halides by Triethylsilane Based on a Cationic Iridium Bis(phosphinite) Pincer Catalyst: Scope, Selectivity and Mechanism
Authors: Yang Jian , Brookhart Maurice 
Published: December 2008

AbstractA highly efficient procedure for the reduction of a broad range of alkyl halides by triethylsilane based on a cationic iridium bis(phosphinite) pincer catalyst has been discovered and developed. This reduction chemistry is chemoselective and has unique selectivities compared with conventional radical‐based processes and the aluminum trichloride/triethylsilane (AlCl3/Et3SiH) and triphenylmethyl tetrakis[pentafluorophenyl]borate/triethylsilane {[Ph3C] [B(C6F5)4]/Et3SiH} systems. Reductions use three equivalents of triethylsilane relative to the halide and can be carried out with very low catalyst loadings and in a solvent‐free manner, which may provide an environmentally attractive and safe alternative to many currently practiced methods for reduction of alkyl halides. Mechanistic studies reveal a unique catalytic cycle. The cationic iridium hydride 2,6‐bis[di‐(tert‐butyl)phosphinyloxy)phenyl(hydrido)iridium, (POCOP)IrH+ {POCOP= 2,6‐[OP(t‐Bu)2]2C6H3} binds and activates the silane. This complex serves as a potent silylating reagent to generate silyl halonium ions, Et3SiXR+, which are reduced by the neutral iridium dihydride to yield alkane product and regenerate the cationic (POCOP)IrH+, thus closing the catalytic cycle. All key intermediates have been identified by in situ NMR monitoring and kinetic studies have been completed. An application of this reduction system to the catalytic hydrodehalogenation of a metal chloride complex is also described.
Kinetic Study of the Asymmetric Hydrogenation of Methyl Acetoacetate in the Presence of a Ruthenium Binaphthophosphepine Complex
Authors: Öchsner Eva , Etzold Bastian , Junge Kathrin , Beller Matthias , Wasserscheid Peter 
Published: December 2008

AbstractThe asymmetric hydrogenation of methyl acetoacetate (MAA) in methanol using dibromobis{(S)‐4‐phenyl‐4,5‐dihydro‐3H‐dinaphtho[2,1‐c: 1′,2′‐e]phosphepine}‐ruthenium was studied in detail. For the determination of the reaction network, data from kinetic experiments were compared to different possible reaction networks using the kinetic software Presto Kinetics. The simulation was optimised to describe the reaction accurately with a minimal set of process parameters and reaction equations. For the best model the reaction orders, collision factors and activation energy of all reaction steps were determined. Additionally, the influence of reaction temperature and hydrogen pressure on the enantiomeric excess (ee) of the reaction was studied. It was found that high reaction temperatures and high hydrogen pressures result in increasing enantioselectivities.
A Dramatic Substituent Effect in Silver(I)‐Catalyzed Regioselective Cyclization of ortho‐Alkynylaryl Aldehyde Oxime Derivatives
Authors: Gao Hongyin , Zhang Junliang 
Published: December 2008

AbstractA 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.
Copper(II)‐Catalyzed CC Bond‐Forming Reactions of α‐Electron‐Withdrawing Group‐Substituted Ketene S,S‐Acetals with Carbonyl Compounds and a Facile Synthesis of Coumarins
Authors: Yuan Hong‐Juan , Wang Mang , Liu Ying‐Jie , Liu Qun 
Published: December 2008

AbstractA new catalytic CC bond‐forming reaction has been developed. Catalyzed by cheap and commercially available copper(II) bromide (CuBr2; 10 mol%), the reactions of α‐electron‐withdrawing group (EWG)‐substituted ketene S,S‐acetals with aldehydes or ketones in acetonitrile at room temperature gave a variety of densely functionalized coupling products in excellent yields (80–98%). Based on this catalytic process, coumarin derivatives were efficiently synthesized when salicylaldehydes were selected as the carbonyl components.
Enantioselective Organocatalytic Michael Addition of α‐Substituted Cyanoacetates to α,β‐Unsaturated Selenones
Authors: Marini Francesca , Sternativo Silvia , Del Verme Francesca , Testaferri Lorenzo , Tiecco Marcello 
Published: December 2008

AbstractA novel enantioselective (up to 90% ee) Michael addition of α‐substituted cyanoacetates to α,β‐unsaturated selenones in the presence of bifunctional urea and thiourea organocatalysts is described. The Michael adducts, containing an all‐carbon quaternary stereocenter, are smoothly converted into synthetically useful polyfunctional compounds by taking advantage of the excellent leaving group ability of the selenone group.
Highly Enantio‐ and Diastereoselective Inverse Electron Demand Hetero‐Diels–Alder Reaction using 2‐AlkenoylpyridineN‐Oxides asOxo‐Heterodienes
Authors: Barroso Santiago , Blay Gonzalo , Muñoz M. Carmen , Pedro José R. 
Published: December 2008

AbstractA general catalytic inverse electron demand hetero‐Diels Alder reaction for 2‐alkenoylpyridineN‐oxides is presented. 2‐AlkenoylpyridineN‐oxides react very efficiently with alkenes in the presence of bisoxazolidine‐copper(II) [BOX‐Cu(II)] complexes to give chiral dihydropyrans bearing a pyridine ring at the 6‐position with very high yields and excellent diastereo‐ and enantioselectivity. These heterodienes exhibited higher reactivity and enantioselectivity than the corresponding non‐oxidized 2‐alkenoylpyridines.
Iron(III) Salt‐Catalyzed Nazarov Cyclization/Michael Addition of Pyrrole Derivatives
Authors: Fujiwara Masamune , Kawatsura Motoi , Hayase Shuichi , Nanjo Masato , Itoh Toshiyuki 
Published: December 2008

AbstractThe Nazarov cyclization of two types of pyrrole derivatives was effectively catalyzed by 5 mol% alumina‐supported iron(III) perchlorate [Fe(ClO4)3⋅Al2O3 ] which provided the desired cyclization with high trans selectivity in good to excellent yield. The cyclized product was next reacted with a vinyl ketone in the presence of the same iron salt to afford the corresponding Michael product. A sequential type Nazarov/Michael reaction of pyrrole derivatives has also been accomplished; the synthetic route to 4,5‐dihydrocyclopenta[b]pyrrol‐6(1 H)‐one derivative 5 or 5,6‐dihydrocyclopenta[b]pyrrol‐4(1 H)‐one derivative 6 has thus been established using a very economical iron catalyst.
Protein adsorption kinetics in charged agarose gels: Effect of agarose content and modeling
Authors: Schirmer Emily B. , Carta Giorgio 
Published: December 2008

AbstractThe adsorption kinetics of myoglobin in charged gels of varying agarose content have been measured macroscopically, through batch uptake experiments, and microscopically, using light microscopy with gels supported in microfluidics chips. The apparent effective pore diffusivities, determined by fitting either set of rate data to the shrinking core model, were greater than the free solution diffusivity and concentration‐dependent. Moreover, the microscopically derived concentration profiles were qualitatively different from the predicted ones. Therefore, a new model taking into account an assumed favorable partitioning of the protein in the pore liquid is proposed to describe the adsorption kinetics. The new model yields effective pore diffusivities that are in approximate agreement with the values determined chromatographically under nonbinding conditions and with hindered diffusion theory. In addition, it predicts concentration profiles in the gel that are consistent with those observed microscopically. The overall increase in mass transfer is attributed to the favorable partitioning of the protein in the pores at low ionic strength, which results in a greater diffusional driving force. © 2008 American Institute of Chemical Engineers AIChE J, 2009
Metal and solvent‐free cyanosilylation of carbonyl compounds with tris(pentafluorophenyl)borane
Authors: Kadam Santosh T. , Kim Sung Soo 
Published: December 2008

AbstractA highly effective method of the cynaosilylation of aldehydes and ketones with TMSCN in the presence of catalytic amount of B(C6F5)3 [tris(pentafluorophenyl)borane] has been developed. Cyano transfer from TMSCN to carbonyl group proceeds at room temperature under solvent‐free conditions. Various alehydes and ketones have been converted into the corresponding trimethylsilylether within short reaction times with excellent yield under mild conditions. Copyright © 2008 John Wiley & Sons, Ltd.
Preparation and permeation characterization of β‐zeolite‐incorporated composite membranes
Authors: Huang Zhen , Su Jun‐Feng , Su Xiao‐Qun , Guo Yu‐Hua , Teng Li‐Jun , Min Yang Chuan 
Published: December 2008

AbstractIn this work, several β‐zeolite‐incorporated polymer composite membranes were fabricated with the solution‐casting method. The zeolite loadings were 10, 20, and 30 wt %, respectively. Scanning electron microscopy characterization showed that the zeolite particles could be uniformly distributed in the whole polymer matrix. Gas permeation results demonstrated that after the incorporation of the same β‐zeolite, the polyimide exhibited a significant increase in gas permeability but a decrease in permselectivity, and both were quite pronounced at high zeolite loadings; this resulted from the loose structure that formed. The poly(ether sulfone) composite membranes showed obvious increases in both permeability and selectivity, and the permeability increase was considerably greater at higher zeolite loadings. The permselectivity increase could possibly be attributed to the pore sieving and preferential adsorption of β‐zeolite entities for the test gases as the heat treatment may have resulted in the formation of a defect‐free microstructure. However, breakthrough of the upper‐bound line was not achieved for these composite membranes, as reflected by Robeson plots. Our results suggest that changes in membrane performance not only are attributable to the properties and content of β‐zeolite particles but also depend on the heterogeneous microstructure created by zeolite entities. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Effect of electron‐beam irradiation on ethylene–methyl acrylate copolymer
Authors: Mongal Nilambar , Chakraborty Debabrata , Bhattacharyya Rupa , Kumar Chaki Tapan , Bhattacharya Pinaki 
Published: December 2008

AbstractEthylene–methyl acrylate copolymer (Elvaloy 1330) was irradiated by an electron beam at different levels of radiation both in the presence and absence of a trimethylolpropane trimethacrylate sensitizer at various dosages of incorporation. The mechanical, thermal, and electrical properties of these samples were compared. The mechanical properties were observed to reach an optimum maximum around 6 Mrad of irradiation and 1 phr of sensitizer incorporation. Furthermore, an increase in either the radiation dose or the sensitizer level helped very little to further modify the properties. The thermal properties as determined by the thermogravimetric analysis and differential scanning calorimetry studies were quite supportive of the observation made during the study of the mechanical properties. The thermal stability of the irradiated samples underwent an increase with increasing electron‐beam dosage. In a manner similar to those of the mechanical properties, the increase in thermal stability was found to reach a maximum at a particular level of treatment and sensitizer incorporation, beyond which there was marginal or no effect at all. The α transition temperature underwent a substantial increase with increasing crosslink density, as evidenced by the increase in gel content with increasing proportion of electron‐beam radiation dose. The other glass‐transition temperature, however, appeared to remain unaffected. The electrical properties, as described by the dielectric constant, volume resistivity, and breakdown voltage, appeared to be affected very little by the electron‐beam radiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Functionalization via glycerol transesterification of polymerized soybean oil
Authors: Lubguban Arnold A. , Tu Yuan‐Chan , Lozada Zuleica R. , Hsieh Fu‐Hung , Suppes Galen J. 
Published: December 2008

AbstractAn acylglycerol‐based molecule was synthesized by the thermal polymerization (bodying) of soybean oil followed by transesterification with glycerol. Transesterification with glycerol at temperatures greater than 200°C provided the desired polyol prepolymers. The extent of bodying and quantity of glycerol added during the transesterification provided tunability of the polyol molecular weight and functionality. The hydroxyl numbers, acidity, and viscosity of the polyols were characterized. The polyols were evaluated in elastomers and rigid foams. Extractability analyses were performed on the polyurethane elastomer wafers to evaluate crosslinking. Rigid foaming results for the processed soy‐based polyol showed excellent physicochemical properties suggesting comparability with a petroleum‐based polyether polyol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Flame‐retardant properties of magnesium hydroxystannate and strontium hydroxystannate coated calcium carbonate on soft poly(vinyl chloride)
Authors: Jiao Yunhong , Xu Jian Zhong 
Published: December 2008

AbstractThe flame‐retardant and smoke‐suppressant properties of soft poly(vinyl chloride) (PVC) treated with zinc hydroxystannate (ZHS), calcium carbonate (CaCO3), magnesium hydroxystannate [MgSn(OH)6], strontium hydroxystannate [SrSn(OH)6], ZHS–MgSn(OH)6, ZHS–SrSn(OH)6, MgSn(OH)6‐coated CaCO3, SrSn(OH)6‐coated CaCO3, ZHS–MgSn(OH)6‐coated CaCO3, and ZHS–SrSn(OH)6‐coated CaCO3 were studied with the limited oxygen index, char yield, and smoke density rating methods; the mechanical properties were also studied. The results showed that, with the equivalent addition of the corresponding hydroxystannate, the soft PVC treated with hydroxystannate‐coated CaCO3 had a higher limited oxygen index than the corresponding hydroxystannate, and the soft PVC treated with the agents containing magnesium had a higher limited oxygen index than the soft PVC treated with the agents containing strontium, except for ZHS–MgSn(OH)6‐coated CaCO3. The improvement in the char formation of the hydroxystannate‐coated CaCO3 was better than that of the corresponding hydroxystannate in most cases, and the aforementioned agents reduced the smoke density rating, decreased the tensile strength, and increased the elongation and impact strength basically. Thermal analysis showed that the additives promoted the evolution of hydrogen chloride, early crosslinking, and rapid charring through the strong catalyzing effect of Lewis acids. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Effects of the nature and combinations of solvents in the intercalation of clay with block copolymers on the properties of polymer nanocomposites
Authors: Şen Sinan , Nugay Nihan , Nugay Turgut 
Published: December 2008

AbstractPolystyrene (PS) nanocomposites were prepared by the free‐radical polymerization of styrene in the presence of organically modified montmorillonite (MMT) clays. MMT clay was modified with a low‐molecular‐weight and quarternized block copolymer of styrene and 4‐vinylpyridine [poly(styrene‐b‐4‐vinylpyridine) (SVP)] with 36.4 wt % PS and 63.6 wt % poly(4‐vinylpyridine) (P4VP). Special attention was paid to the modification, which was carried out in different compositions of a solvent mixture of tetrahydrofuran (THF) and water. The swelling behavior of the MMT clay was studied by an X‐ray diffraction technique. The diffraction peak shifted to lower 2θ angles for all of the modified clays, which indicated the intercalation of the quarternized SVP copolymer into the MMT layers in different degrees. Higher interlayer distances, which showed a high degree of block copolymer insertion, were obtained for solvent compositions with THF in water. The resultant nanocomposites were characterized by X‐ray diffraction, atomic force microscopy, scanning electron microscopy, thermogravimetric analysis, and dynamic mechanical analysis. The desired exfoliated nanocomposite structure was achieved when the MMT modification was conducted in 50 or 66 wt % THF, whereas the other modifications all resulted in intercalated structures. The resulting exfoliated nanocomposite was found to have better thermal stability and dynamic mechanical performance compared to the others, even with 2% clay loading. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Design engineers and technical professionals at work: Observing information usage in the workplace
Authors: Allard Suzie , Levine Kenneth J. , Tenopir Carol 
Published: December 2008

AbstractThis exploratory study examines how design engineers and technical professionals (hereafter referred to as engineers) in innovative high‐tech firms in the United States and India use information in their daily work activities including research, development, and management. The researchers used naturalistic observation to conduct a series of daylong workplace observations with 103 engineers engaged in product design and testing in four U.S.‐ and two India‐based firms. A key finding is that engineers spend about one fourth of their day engaged in some type of information event, which was somewhat lower than the percentage identified in previous research. The explanation may be rooted in the significant change in the information environment and corporate expectations in the last 15 years, which is the time of the original study. Searching technology has improved, making searching less time consuming, and engineers are choosing the Internet as a primary source even though information may not be as focused, as timely, or as authoritative. The study extends our understanding of the engineering workplace, and the information environment in the workplace, and provides information useful for improving methods for accessing and using information, which could ultimately lead to better job performance, facilitate innovation, and encourage economic growth.
Chiral Guanidine Catalyzed Enantioselective Reactions
Authors: Leow Dasheng , Tan Choon‐Hong 
Published: December 2008

AbstractPinches like a crab: The utilization of guanidines as catalysts has been growing at a steady pace. They possess high pKa values and activate through dual hydrogen‐bonding modes of activation. This Focus Review highlights the development of chiral guanidine catalysts in asymmetric organic transformations.magnified imageChiral guanidine catalysts share common characteristics such as high pKa values and dual hydrogen‐bonding modes of activation, and high catalytic activities and enantioselectivities can often be achieved. The utilization of guanidines as catalysts has been growing at a steady pace. In the past few years, it has attracted tremendous attention through several landmark achievements. This article highlights the development of chiral guanidine catalysis in asymmetric synthesis.
Transition‐Metal‐Catalyzed Enantioselective [2+2+2] Cycloadditions for the Synthesis of Axially Chiral Biaryls
Authors: Tanaka Ken 
Published: December 2008

AbstractTying up loose ends: Recent advances towards a development of novel transition‐metal‐catalyzed enantioselective [2+2+2] cycloadditions for the synthesis of biaryls are summarized in this Focus Review. Additionally, the enantioselective synthesis of axially chiral biaryls possessing non‐biaryl axial chirality is also presented. These novel asymmetric aromatization reactions allow the production of various axially chiral biaryl compounds with high enantioselectivity.magnified imageRecent advances towards a development of novel transition‐metal‐catalyzed enantioselective [2+2+2] cycloadditions for the synthesis of axially chiral biaryls are reviewed. A number of efficient enantioselective biaryl syntheses were accomplished by chiral cobalt(I), iridium(I), and rhodium(I) complex catalyzed [2+2+2] cycloadditions. Furthermore, the enantioselective synthesis of axially chiral biaryls possessing non‐biaryl axial chirality was also developed by using chiral rhodium(I) complexes as catalysts.
First passage time for multivariate jump‐diffusion processes in finance and other areas of applications
Authors: Zhang Di , Melnik Roderick V. N. 
Published: December 2008

AbstractThe first passage time (FPT) problem is an important problem with a wide range of applications in science, engineering, economics, and industry. Mathematically, such a problem can be reduced to estimating the probability of a stochastic process first to reach a boundary level. In most important applications in the financial industry, the FPT problem does not have an analytical solution and the development of efficient numerical methods becomes the only practical avenue for its solution. Most of our examples in this contribution are centered around the evaluation of default correlations in credit risk analysis, where we are concerned with the joint defaults of several correlated firms, the task that is reducible to a FPT problem. This task represents a great challenge for jump‐diffusion processes (JDP). In this contribution, we develop further our previous fast Monte Carlo method in the case of multivariate (and correlated) JDP. This generalization allows us, among other things, to evaluate the default events of several correlated assets based on a set of empirical data. The developed technique is an efficient tool for a number of financial, economic, and business applications, such as credit analysis, barrier option pricing, macroeconomic dynamics, and the evaluation of risk, as well as for a number of other areas of applications in science and engineering, where the FPT problem arises. Copyright © 2008 John Wiley & Sons, Ltd.