bluuebunny/crossref_metadata_2025_split huggingface dataset:
Asymmetric catalytic synthesis of polyketones and polycarbonates
Authors: Nozaki K. 
Published: October 2007

Abstract
Two examples are presented for the synthesis of optically active polymers with main-chain chirality from achiral monomers using chiral metal-complexes as catalysts. Asymmetric alternating copolymerization of α-olefins with carbon monoxide provided optically active polyketones when catalyzed by an (R,S)-BINAPHOS-Pd complex. From propene and CO, highly isotactic polyketone with high enantioselectivity (>97 % like diad and >95 % ee). Spectroscopic and theoretical studies revealed that the olefin insertion is the key step for the enantiofacial selection and that this step takes place at cis to the phosphine part of (R,S)-BINAPHOS. The catalyst is applicable not only to propene/CO but also to styrene/CO, which enabled the first asymmetric terpolymerization of propene/styrene/CO. The catalyst tolerates funational groups such as fluorocarbons and a nitrile group so that they can be incorporated in the side chain. Optically active polycarbonate was also synthesized by the alternating copolymerization of cyclohexene oxide with carbon dioxide via the desymmetrization of the meso-epoxide. Dinuclei zinc species prepared from diethylzinc, ethanol, and α,α'-diphenylprolinol, was revealed to be the real active species.
Development of a new methodology for the preparation of optically active alcohols
Authors: Andersson P. G. 
Published: October 2007

Abstract
This article summarizes our recent achievements in the asymmetric catalytic formation of chiral alcohols using 3-substituted, 2-azanorbornyl-based ligands. The use of this structural unit in ligand synthesis offers several advantages over the analogous proline chemistry, such as equal availability of both enantiomers and increased rigidity of the catalysts. This ligand has been found to be very useful for the two reactions described in this paper: the ruthenium-catalyzed transfer hydrogenation of ketones, and the base-mediated rearrangement of epoxides.
Stereochemistry of epoxide carbonylation using bimetallic Lewis acid/metal carbonyl complexes
Authors: Getzler Y. D. Y. L. , Mahadevan Viswanath , Lobkovsky E. B. , Coates G. W. 
Published: October 2007

Abstract
The stereochemistry of epoxide carbonylation using bimetallic [Lewis acid]+[Co(CO)4]- complexes is reported. The achiral complex [(salph)Al(THF)2][Co(CO)4] stereospecifically carbonylates cis- and trans-2-butene oxide to the trans- and cis-β-lactones, respectively. Preliminary experiments regarding the carbonylative kinetic resolution of racemic trans-2-butene oxide using the enantiomerically pure complex [(R,R-salcy)Al(THF)2][Co(CO)4] are also reported.
Dual role of nucleophiles in palladium-catalyzed Heck, Stille, and Sonogashira reactions
Authors: Jutand Anny 
Published: October 2007

Abstract
In palladium-catalyzed Heck, Stille, or Sonogashira reactions, the nucleophiles-respectively, alkenes, vinylstannanes, or alkynes-are involved in carbopalladation or transmetallation steps that follow the oxidative addition of an aryl halide or triflate to a Pd0 complex. As soon as the nucleophiles possess a C=C or a C 'triple-bond' C bond capable of coordinating the Pd0 complex active in the oxidative addition, they play a dual role since they interfere in the oxidative addition by a decelerating effect due to a partial coordination of the active Pd0 complex. Indeed, its concentration decreases due to the formation of either unreactive complexes (η2-RCH=CH2)Pd0L2 (R = Ph, CO2Et, L = PPh3 ; R = Bu3Sn, L = AsPh3), (η2-RCH=CH2)Pd0L2(OAc)- (R = Ph, L = PPh3), (η2-R-C 'triple-bond' CH)Pd0L2 (R = Ph, L = PPh3) or more slowly reactive complexes (η2-R-C 'triple-bond' CH)Pd0L2 (R = CO2Et, L = PPh3), (η2-RCH=CH2)Pd0L2 (R= CO2Me, L2 = dppf). Whenever the oxidative addition is faster than the ensuing carbopalladation or transmetallation, the decelerating effect of the nucleophiles in the oxidative addition is in favor of a better efficiency for the catalytic cycle by bringing the rate of the fast oxidative addition closer to that of the slow carbopalladation or transmetallation steps.
Coordination of the Trost modular ligand to palladium allyl fragments: Oligomers, monomers and memory effects in catalysis
Authors: Lloyd-Jones G. C. , Stephen S. C. , Fairlamb I. J. S. , Martorell Aina , Dominguez Beatriz , Tomlin P. M. , Murray M. , Fernandez J. M. , Jeffery J. C. , Riis-Johannessen T. , Guerziz Toufik 
Published: October 2007

Abstract
Reaction of the C
2-symmetric "Trost modular ligand" with cationic Pd(II) allyl fragments allows isolation of air- and bench-stable pro-catalysts for the asymmetric allylic alkylation of racemic cycloalkenyl esters. In solution, three distinct complexation modes are observed. When mixed in a ligand/Pd ratio of 1/2, a binuclear bis-P,O-chelate complex is generated. This species does not induce enantioselectivity in the reaction. In contrast, with a ligand/Pd ratio of 1/1, a highly enantioselective, P,P-coordinated pro-catalyst system is generated in which there are two basic coordination modes: monomeric and oligomeric. The monomeric form is mononuclear and exists as two 13-membered chelates, isomeric through loss of C
2-symmetry in the ligand. The oligomeric form is polynuclear and forms chains and rings of alternating ligand and cationic Pd(allyl) units, one of which was identified by single-crystal X-ray diffraction. In solution, the monomeric and oligomeric species are in dynamic equilibrium with populations and interconversion rates controlled by concentration, temperature, and counterion. Isotopic desymmetrization analysis suggests that the monomer-oligomer equilibrium plays a crucial role in both the selectivity and efficiency of the asymmetric allylic alkylation reaction.
New methods for the synthesis of heterocyclic compounds
Authors: Caiazzo Aldo , Dalili Shadi , Picard C. , Sasaki M. , Siu T. , Yudin A. K. 
Published: October 2007

Abstract
Due to frequent occurrence of nitrogen-containing groups among the biologically active compounds, chemoselective functionalization of organic molecules with nitrogen-containing functional groups is an important area of organic synthesis. We have proposed and implemented a new strategy toward design of nitrogen-transfer reactions on inert electrode surfaces with a particular focus on the generation and trapping of highly reactive nitrogen-transfer agents. A wide range of structurally dissimilar olefins can be readily transformed into the corresponding aziridines. The resulting aziridines are precursors to a range of catalysts via nucleophilic ring-opening with diaryl- and dialkyl phosphines. Another strategy explored in the context of oxidative nitrogen transfer is cycloamination of olefins using NH aziridines.
Mechanistic insights into perfluoroaryl borane-catalyzed allylstannations: Toward asymmetric induction with chiral boranes
Authors: Morrison D. J. , Blackwell J. M. , Piers W. E. 
Published: October 2007

Abstract
The perfluoroaryl borane B(C6F5)3 is an effective catalyst for a variety of organic transformations. In the hydrosilation of carbonyl functions, it activates the silane rather than the carbonyl substrate. In allylstannation reactions, two competing reaction pathways are observed, one involving tin cation catalysis, the other "true" borane catalysis. For B(C6F5)3, the former mechanism dominates, while for the weaker Lewis acid PhB(C6F5)2, the latter pathway is more prominent. Thus, chiral boranes of similar Lewis acid strength to PhB(C6F5)2 have the potential to mediate asymmetric allylstannation of aldehyde substrates.
New insights into the mechanism of molybdenum-catalyzed asymmetric alkylation
Authors: Krska S. W. , Hughes D. L. , Reamer R. A. , Mathre D. J. , Palucki M. , Yasuda Nobuyoshi , Sun Y. , Trost B. M. 
Published: October 2007

Abstract
The major features of the catalytic cycle, including structures of key intermediates, have been determined for the molybdenum-catalyzed asymmetric alkylation. The crystal structure of the π-allyl intermediate exhibits 3-point binding of an anionic ligand. Based on NMR analysis, this species adopts in solution a structure consistent with that observed in the solid state. For the allylic alkylation, the crystal structure predicts the opposite stereochemistry vs. that observed experimentally, which suggests that either the reaction proceeds via a minor isomer (Curtin-Hammett conditions) or with retention of configuration. In addition, CO transfer, promoted by Mo(CO)6, has been found to play a key role in catalyst turnover.
Recent advances in catalyst immobilization using supercritical carbon dioxide
Authors: Leitner Walter 
Published: October 2007

Abstract
Homogeneous organometallic catalysts have a great potential for the development of sustainable synthetic processes. There is, however, an urgent need for the development of new techniques to separate products and catalysts efficiently, allowing for recycling and reuse of the precious catalyst. The unique solvent properties of supercritical carbon dioxide offer new approaches for the immobilization of organometallic catalysts, many of which are suitable for efficient continuous-flow operation. Recent research in this field tries to combine the molecular nature of organometallic catalysts with the reaction-engineering aspect of multiphase catalysis.
Substrate scope in the olefin cyclopropanation reaction catalyzed by m-oxo-bis[(salen)iron(III)] complexes
Authors: Edulji S. K. , Nguyen S. T. 
Published: October 2007

Abstract
The cyclopropanation of various alkenes with different diazoester compounds was investigated using two different μ-oxo-bis[(salen)iron(III)] complexes, [Fe(3,3',5,5'-
t
Bu4salen)]2O and [Fe(salen)]2O. Ethyl diazoacetate (EDA), tert-butyl diazoacetate (
t
BDA), and ethyl diazoacetoacetate (EDAA) were used with mono- and disubstituted terminal olefins (styrene and 1,1-diphenyl ethylene, respectively), internal olefin (trans-β-methyl styrene), and an electron-rich alkene (n-butyl vinyl ether). Moderate-to-good cyclopropanation yields were obtained for most substrates.
Recent advances in transition metal-catalyzed or -mediated cyclization of 2,3-allenoic acids: New methodologies for the synthesis of butenolides
Authors: Ma S. 
Published: October 2007

Abstract
The cyclization reactions of 2,3-allenoic acids or their salts with optically active bases affording butenolides are discussed. Two reaction pathways were observed: (1) intermolecular carbometallation-intramolecular allylation; (2) cyclic oxymetallation-reductive elimination. High efficiency of chirality transfer was realized with the latter case.
3-Halopropenyl esters as precursors of a new class of oxygen-substituted allylic organometallic compounds: Applications in organic synthesis
Authors: Lombardo Marco , Licciulli Sebastiano , Trombini C. 
Published: October 2007

Abstract
3-halopropenyl esters, readily prepared by the addition of acyl halides to acrolein, react with zinc, indium, and chromium(II), thus opening a route to a new class of oxygen-substituted allylic organometallic compounds. Indium and zinc reagents smoothly add to carbonyl compounds, affording alk-1-en-3,4-diol derivatives in a variety of synthetic procedures which include typical Grignard stepwise conditions as well as Barbier one-pot protocols. Using zinc and indium in water or aprotic solvents, simple diastereoselectivity was found to depend on the nature of the carbonyl compound; conjugated aldehydes favor formation of syn-adducts while unconjugated aldehydes favor anti-adducts. Moving to chromium, a reversal of regioselectivity was observed in favor of (Z)-4-hydroxy-enolacetates, flexible protected forms of homoaldols. Chromium complexes are generated in a catalytic cycle based on the combined use of the redox Mn(0)/Cr(III) couple and of TMSCl. When the Cr-catalyzed reaction is carried out in the presence of Jacobsen's Salen ligand, the regiochemical outcome of the reaction is again reversed, and syn-alk-1-en-3,4-diols are formed in high ee's.
Palladium-catalyzed alkylation of unactivated olefins
Authors: Widenhoefer Ross A. 
Published: October 2007

Abstract
The reaction of a 3-butenyl β-diketone with a catalytic amount of PdCl2(CH3CN)2 in dioxane at room temperature led to olefin hydroalkylation and formation of the corresponding 2-acylcyclohexanone in good yield as a single regioisomer. Deuterium-labeling experiments for the hydroalkylation of 7-octene-2,4-dione were in accord with a mechanism involving outer-sphere attack of the pendant enol on a palladium-complexed olefin to form a palladium cyclohexyl species, followed by palladium migration via iterative β-hydride elimination/addition and protonolysis from a palladium enolate complex. In comparison to a 3-butenyl β-diketone, reaction of a 4-pentenyl β-diketone with a catalytic amount of PdCl2(CH3CN)2 in the presence of CuCl2 led to oxidative alkylation and formation of the corresponding 2-acyl-3-methyl-2-cyclohexenone in good yield as a single isomer. Unactivated olefins tethered to less reactive carbon nucleophiles such as β-keto esters, α-aryl ketones, and even dialkyl ketones underwent palladium-catalyzed hydroalkylation in the presence of Me3SiCl or HCl to form the corresponding cyclohexanones in moderate-to-good yield with high regioselectivity.
Heterogeneous asymmetric catalysis
Authors: Lemaire Marc 
Published: October 2007

Abstract
Examples of enantioselective catalysts, including homogeneous supported catalysts and biphasic liquid/liquid, are described and compared. In the case of asymmetric hydride transfer, polythiourea was proven to be more efficient for ruthenium-catalyzed reduction of arylketones, although the iridium complexes gave rise to higher ee when using amino sulfonamide bound to a polystyrene matrix. In the case of asymmetric reduction, the modification of the binap allows the formation of a polymer that could be used as a catalyst precursor and exhibits enantioselectivities as high as observed in solution, but easier to separate and recycle. Bisoxazoline bound to silica particules could also be used in copper-catalyzed asymmetric Diels-Alder reaction and cyclopropanation with selectivities similar to that obtained in solution.
Stereoselective chromium- and molybdenum-mediated transformations of arenes
Authors: Kündig E. P. , Cannas Rita , Fabritius C.-H. , Grossheimann Gabriele , Kondratenko Mikhail , Laxmisha Mundruppady , Pache S. , Ratni H. , Robvieux F. , Romanens P. , Tchertchian S. 
Published: October 2007

Abstract
Tricarbonylchromium-mediated dearomatization provides a rapid access to substituted cyclohexadienes. Efficient asymmetric routes to planar chiral arene complexes and to substituted cyclohexadienes have been developed. The article sums up the main features of this chemistry. Highly enantiomerically enriched ortho-substituted benzaldehyde complexes are accessible via asymmetric lithiation followed by trapping with electrophiles. In different solvents, the trimethylsilyl complex exhibits [alpha] values ranging from −174 to +108 for the same enantiomer. Details of two asymmetric syntheses of natural products are given: the alkaloid lasubine I starting from a highly enantiomerically enriched planar chiral arene complex and the marine furanosesquiterpene acetoxytubipofuran. The latter is assembled via asymmetric dearomatization of a benzaldehyde imine complex. Other key steps include an Eschenmoser–Claisen rearrangement and a regio- and diastereoselective Pd-catalyzed allylic substitution. The final section deals with labile arene metal complexes. For the first time, dearomatization reactions mediated by the Mo(CO)3 group have been realized. The reactions show strong analogies to the Cr(CO)3-mediated reactions, but exhibit also marked differences: the arene–Mo bond is stronger, but more labile, and the sequential double additions show different selectivities compared to the chromium analogs.
Voltammetry of drugs at the interface between two immiscible electrolyte solutions
Authors: Alemu Hailemichael 
Published: October 2007

Abstract
In this review, the results of the electrochemical investigations made on the transfer of ionizable drugs at the interface between two immiscible electrolyte solutions (ITIES) in the last decade have been presented. In many of the studies, cyclic voltammetry has been used to investigate the transfer characteristics of the charged species and deduce their partition coefficients, which are very important parameters to infer the lipophilicity of drugs in biological systems. The electrochemical technique allows the precise determination of the distribution of ionic species between two phases in a wider pH range. Such studies point out the complexity of the distribution of ionizable compounds and offer a new approach to relate the structure of such compounds to their passive transport across biological membranes.
Why liquid membrane extraction is an attractive alternative in sample preparation
Authors: Chimuka Luke , Cukrowska Ewa , Jönsson J. Å. 
Published: October 2007

Abstract
The use of liquid membrane-based extractions is increasingly seen as offering an alternative to conventional sample preparation procedures in analysis of chemical species in both environmental and biological media. In this article, emphasis is placed on the attractiveness of liquid membrane-based extraction techniques to a variety of analytical applications such as speciation of metal ions in biological fluids, time-weighted average field sampling, and time-weighted average passive field sampling. Further, the area of designing new and much simpler miniaturized configurations, which is enjoying much attention in liquid membrane-based extraction techniques, is discussed.
Biosensors for environmental applications: Future development trends
Authors: Rodriguez-Mozaz S. , Marco M.-P. , de Alda M. J. Lopez , Barceló D. 
Published: October 2007

Abstract
Biosensors can be excellent analytical tools for monitoring programs working to implement legislation. In this article, biosensors for environmental analysis and monitoring are extensively reviewed. Examples of biosensors for the most important families of envi-ronmental pollutants, including some commercial devices, are presented. Finally, future trends in biosensor development are discussed. In this context, bioelectronics, nanotechnology, miniaturization, and especially biotechnology seem to be growing areas that will have a marked influence on the development of new biosensing strategies in the next future.
Protein adsorption to planar electrochemical sensors and sensor materials
Authors: Lim Caroline , Slack S. , Ufer S. , Lindner E. 
Published: October 2007

Abstract
In electrochemical sensing devices, aimed for acute and chronic in vivo application, the active surface of the sensor is often negligible compared to the overall surface area of the device in contact with the biological host. Consequently, to minimize the perturbation of an implanted sensor on the in vivo environment the chemical composition and surface texturing of the complete device (the active sensor, sensor substrate, and “accessories”) have to be considered. In our work, the adsorption of three abundant proteins (albumin, IgG, and fibrinogen) was determined quantitatively on untreated and modified sensor substrates and sensing membrane surfaces. In this study, a flexible polyimide-based material (Kapton ®) was used as sensor substrate with or without an amorphous diamond-like carbon (DLC) or an amorphous oxygen-containing DLC (o-DLC) coating. The ion-sensitive membranes were cast from high-molecular-weight (HMW) or carboxylated poly(vinyl chloride) (PVC) and were doped with increasing concentrations of highly hydrophilic poly(ethylene oxide) (PEO). The potentiometric characteristics of the potassium-selective membranes cast with up to 6 % PEO were the same as those without PEO. However, the PEO-modified PVC membranes elicited a large amount of protein adsorption, especially in terms of albumin.
Glutamate oxidase advances in the selective bioanalytical detection of the neurotoxic amino acid β-ODAP in grass pea: A decade of progress
Authors: Moges G. , Wodajo N. , Gorton L. , Yigzaw Yirgalem , Kalcher Kurt , Belay Abebaw , Akalu Girma , Nair B. M. , Solomon T. 
Published: October 2007

Abstract
The search for an enzyme as a reagent for selective bioanalytical detection of the neurotoxic amino acid, β-N-oxalyl L-alpha, β-diaminopropionic acid, β-ODAP (found in grass pea, Lathyrus sativus) led to its redox catalytic reaction by glutamate oxidase (GluOx). Homogeneous kinetic studies and an immobilized GluOx reactor-based flow-injection assay were initially made for beta-ODAP with small immobilized GluOx/catalase glutamate destroying prereactors. The method was applied to examine the toxin content in processed grass pea. The kinetics and the equilibrium of the thermal isomerization of β-ODAP to the nontoxic isomer α-ODAP established that GluOx is specific to the neurotoxin. The first ever GluOx-based amperometric biosensor for liquid chromatography (LC) detection was reported in 1997. This biosensor coupled with a refractive index detector improved LC performance. The most recent work with GluOx resulted in MnO2-based screen-printed amperometric biosensor, with offline elimination of glutamate interference by glutamate decarboxylase. A single-shot chemiluminescent sensor developed for hydrogen peroxide is also proposed for β-ODAP with GluOx application. This decade of progress resulted from studies that included four Ph.D. (Ethiopia, Sweden, Austria), four M.Sc. (Ethiopia, Sweden) and Licentiate (Sweden) theses projects, plus one collaborative project in Sweden. The advances in grass pea research may be regarded as a model north–south cooperation for research and education.
Immobilized peptides/amino acids on solid supports for metal remediation
Authors: Malachowski Lisa , Stair J. L. , Holcombe J. A. 
Published: October 2007

Abstract
Recently,a significant amount of work has focused on metal binding by natural systems for various applications. This review will focus on the utility of amino acids, short peptides, and proteins that have been immobilized onto solid supports for use in metal binding. These systems include single amino acids, poly-amino acids, and peptides immobilized onto supports such as silica, polymer resins, and membranes. Also included are the studies involving the use of immobilized amino acids in ion-exchange chromatography.
Electrochemistry and application of a novel monosubstituted squarate electron-transfer mediator in a glucose oxidase-doped poly(phenol) sensor
Authors: Iwuoha E. I. , Williams-Dottin A. R. , Hall L. A. , Morrin A. , Mathebe G. N. , Smyth M. R. , Killard Anthony 
Published: October 2007

Abstract
Electrosynthetic poly(phenol) nanofilms were deposited in situ on platinum electrodes in the presence and absence of glucose oxidase. The synthesis charges and currents of the nonconducting polymer films were recorded at various applied potentials for films grown from 25 –100 mM phenol concentrations. Film parameters such as the standard rate constant for film deposition, film thickness, and surface concentration of the poly(phenol) films were evaluated from the cyclic and step voltammograms of the polymerization process. A novel electron-transfer mediator consisting of monosubstituted 4-hydroxycyclobut-3-ene-1,2-dione (squarate) was used as a mediator for Pt/poly(phenol) nanofilm/GOx amperometric glucose biosensors. Amperometric responses for 3-diphenylamino-4-hydroxycyclobut-3-ene-1,2-dione (diphenylaminosquarate: E°'=of +328 mV/Ag-AgCl at pH 7.0)-mediated systems were measured by both steady-state amperometric and cyclic voltammetry. The sensor sensitivity was calculated to be 558 nA cm−2 (µM)−1.