bluuebunny/crossref_metadata_2025_split huggingface dataset:
Substrate‐Controlled Highly Diastereoselective Synthesis of Primary and Secondary Diorganozinc Reagents by a Hydroboration/Boron–Zinc Exchange Sequence
Authors: Hupe Eike , Calaza M. Isabel , Knochel Paul 
Published: June 2003

AbstractThe scope of substrate‐controlled diastereoselective hydroborations can be considerably enhanced by a boron–zinc exchange reaction, providing organozinc derivatives that react with a broad range of electrophiles. Even normally unreactive boronic esters, obtained by Rh‐catalyzed hydroboration with catecholborane, react readily with iPr2Zn providing the corresponding zinc reagents in high diastereoselectivity.
Hybrid Organic–Inorganic 1D and 2D Frameworks with ε‐Keggin Polyoxomolybdates as Building Blocks
Authors: Dolbecq Anne , Mialane Pierre , Lisnard Laurent , Marrot Jérôme , Sécheresse Francis 
Published: June 2003

AbstractOrganic–inorganic hybrid materials based on polyoxometalate building blocks with capping La3+ ions and bidentate oxygenated ligands have been obtained by reaction at room temperature of the [ε‐PMo12O36(OH)4{La(H2O)4}]5+ polyoxocation with glutarate (C5H6O22−) and squarate (C4O42−) organic ligands. [ε‐PMo12O37(OH)3{La(H2O)4(C5H6O4)0.5}4]⋅21 H2O (1) and [ε‐PMo12O39(OH){La(H2O)6}2{La(H2O)5(C4O4)0.5}2]⋅17 H2O (2) form unprecedented 1D chains built from alternating polyoxocations and organic ligands connected through LaO links. The structures of these materials are compared to the 2D hybrid organic–inorganic framework [NC4H12]2[Mo22O52(OH)18{La(H2O)4}2{La(CH3CO2)2}4]⋅8 H2O (3) isolated from the hydrothermal reaction of elemental precursors (MoO42−, Mo, La3+) in acetate buffer. Compound 3 is built from previously undescribed polyoxometalate units with twenty‐two MoV centers capped by six La3+ ions, four of which are bridged by acetate ligands.
Highly Diastereoselective [3+2] Cycloadditions between Nonracemic p‐Tolylsulfinimines and Iminoesters: An Efficient Entry to Enantiopure Imidazolidines and Vicinal Diaminoalcohols
Authors: Viso Alma , Fernández de la Pradilla Roberto , García Ana , Guerrero‐Strachan Carlos , Alonso Marta , Tortosa Mariola , Flores Aida , Martínez‐Ripoll Martín , Fonseca Isabel , André Isabelle , Rodríguez Ana 
Published: June 2003

AbstractA new procedure for the asymmetric synthesis of imidazolidines and vicinal diamines is reported. The 1,3‐dipolar cycloaddition between nonracemic p‐tolylsulfinimines and azomethine ylides generated in situ from α‐iminoesters and LDA produces N‐sulfinylimidazolidines with a high degree of stereocontrol. In contrast, the presence of Lewis acids promotes formation of the cycloadducts through a highly diastereoselective process with opposite stereochemistry. Subsequent transformations of the imidazolidines including oxidative, reductive, and hydrolytic processes that provide easy access to vicinal diaminoalcohols have been explored. Among these, reductive cleavage of the aminal with LiAlH4 is an extremely efficient and general reaction for the synthesis of enantiopure N‐sulfinyl‐N′‐benzyldiaminoalcohols.
Synthesis of Enantiomerically Enriched Propargylamines by Copper‐Catalyzed Addition of Alkynes to Enamines
Authors: Koradin Christopher , Gommermann Nina , Polborn Kurt , Knochel Paul 
Published: June 2003

AbstractThe first copper(I) bromide/Quinap‐catalyzed synthesis of enantiomerically enriched propargylamines by addition of alkynes to enamines is reported. Various functionalized terminal alkynes add smoothly to Nprotected enamines to afford the corresponding amines in good to high yields and moderate to good enantiomeric excesses. The influence of the metal salt, the ligand, and the protecting group on the conversion, the reaction rate, and the stereoselectivity of the reaction are investigated. The scope of the reaction and further transformations of the resulting propargylamines (deprotection, Pauson–Khand reaction) are also described.
Laser Spectroscopic Studies of Interactions of UVI with Bacterial Phosphate Species
Authors: Knopp Roger , Panak Petra J. , Wray Lewis A. , Renninger Neil S. , Keasling Jay D. , Nitsche Heino 
Published: June 2003

AbstractWe have investigated the interactions of UVI with two bacterial phosphate‐containing species: Gram‐positive Bacillus sphaericus and Gram‐negative Psedomonas aeruginosa. The Gram‐positive B. sphaericus was investigated by using Raman spectroscopy and time‐resolved laser‐induced fluorescence spectroscopy (TRLFS). We found that living cells, spores, and intact heat‐killed cells complexed UVI (pH 4.5) through phosphate groups bound to their surfaces, while decomposed cells released H2PO4− and precipitated UVI as UO2(H2PO4)2. TRLFS of UVI showed that Gram‐negative P. aeruginosa—genetically engineered to accumulate polyphosphate, subsequently degrade it, and secrete phosphate—precipitated UVI quantitatively at pH 4.5. The same bacterial strain, not induced to secrete phosphate, sorbed only a small amount of UVI.
The Carbon Skeleton of the Belt Region of Fullerene C84 (D2)
Authors: Neudorff Wolf Dietrich , Lentz Dieter , Anibarro Maribel , Schlüter A. Dieter 
Published: June 2003

AbstractThe synthesis and structural characterization of the double‐stranded carbon skeleton in the belt region of a C84 fullerene has been achieved. The synthetic methodology used is based on cyclic dimerization of diastereomeric AB‐type monomers 18 by a non‐diastereospecific Diels–Alder reaction with isobenzofuran and acenaphthylene groups as reactive termini. Four diasteromeric monomer precursors 17 were prepared for the first time by the use of dihydropyracylene (12) in a multistep synthesis. The synthesis of dihydropyracylene itself has been optimized to the degree that it is now available on the 10 g scale. The belt‐shaped macrocycle 19, obtained from dimerization of the monomers 17, could be partly aromatized by an acid‐catalyzed dehydration reaction to give 23, which differs from the fully unsaturated belt by two “water” molecules. Semiempirical AM1 calculations of the electronic and thermodynamic properties of cyclic fluoranthenes revealed strain energy as the essential reason for the incomplete aromatization of 19. The structures of the macrocycles 19 and 23, one of the monomer precursors, and two diastereomeric epoxybenzo[k]fluoranthenes were elucidated by single‐crystal Xray crystallography.
MTO and OsO4: An Efficient Catalytic Couple for Mild H2O2‐Based Asymmetric Dihydroxylation of Olefins
Authors: Jonsson Sandra Y. , Adolfsson Hans , Bäckvall Jan‐E. 
Published: June 2003

AbstractA novel and robust system for osmium‐catalyzed asymmetric dihydroxylation of olefins by aqueous H2O2 with methyltrioxorhenium (MTO) as electron transfer mediator (ETM) has been developed. The MTO is catalyzing the H2O2 oxidation of the chiral ligand to its mono‐N‐oxide, which in turn reoxidizes OsVI to OsVIII. Thus the (DHQD)2PHAL plays a dual role serving as the chiral inductor as well as the tertiary amine generating the N‐oxide required for the recycling of osmium. The present catalytic system gives vicinal diols in good isolated yields and high enantiomeric excess (up to 99 % ee).
Controlling the Conformation and Interplay of p‐Sulfonatocalix[6]arene as Lanthanide Crown Ether Complexes
Authors: Dalgarno Scott J. , Hardie Michaele J. , Makha Mohamed , Raston Colin L. 
Published: June 2003

AbstractControl over the conformational flexibility of p‐sulfonatocalix[6]arene in the solid state is possible in the presence of varied stoichiometric amounts of [18]crown‐6 and selected lanthanide(III) chlorides. Complexes 1 and 2 have the calixarene in the elusive “up–up” double cone conformation, whilst complex 3 has the calixarene in the centrosymmetric “up–down” double partial cone conformation, whereby it acts as a divergent receptor. Complex 1 has a double “molecular capsule” arrangement which is composed of two p‐sulfonatocalix[6]arenes shrouding two [18]crown‐6 molecules, also with both coordinated and homoleptic aquated lanthanide ions around the hydrophilic sulfonate rims of the calixarenes. Complex 2 has a “ferris wheel” arrangement with one lanthanide metal centre coordinated to a sulfonate group and another coordinated to the crown ether whilst tethered to a sulfonate group of the calixarene. Complex 3 forms from a solution with large excess of [18]crown‐6, and possesses a crown ether molecule in each of the partial cones and has homoleptic aquated lanthanide ions involved in a complicated hydrogen‐bonding regime within the extended structure.
Polynitrogen Chemistry: Preparation and Characterization of (N5)2SnF6, N5SnF5, and N5B(CF3)4
Authors: Wilson William W. , Vij Ashwani , Vij Vandana , Bernhardt Eduard , Christe Karl O. 
Published: June 2003

AbstractMetathetical processes were used to convert N5SbF6 into N5[B(CF3)4] and (N5)2SnF6. The latter salt is especially noteworthy because it contains two N5+ ions per anion, thus demonstrating that salts with touching polynitrogen cations can be prepared. This constitutes an important milestone towards our ultimate goal of synthesizing a stable, ionic nitrogen allotrope. The stepwise decomposition of (N5)2SnF6 yielded N5SnF5. Multinuclear NMR spectra show that in HF the SnF5− ion exists as a mixture of Sn2F102− and Sn4F204− ions. Attempts to isolate FN5 from the thermolysis of (N5)2SnF6 were unsuccessful, yielding only the expected decomposition products, FN3, N2, trans‐N2F2, NF3, and N2.
Cover Picture: The Synthesis of Carboracycles Derived from B,B′‐Bis(aryl) Derivatives of Icosahedral ortho‐Carborane (Chem. Eur. J. 12/2003)
Authors: Bayer Michael J. , Herzog Axel , Diaz Martin , Harakas George A. , Lee Hans , Knobler Carolyn B. , Hawthorne M. Frederick 
Published: June 2003

AbstractThe cover picture shows a space‐filling model of a macrocycle consisting of four bis‐aryl‐substituted icosahedral ortho‐carborane modules that are tethered with propylene linkers (carbon: gray, boron: green, hydrogen: white). All eight para‐functionalized aryl groups are attached to a propylene chain carrying a terminal sulfonate group (sulfur: yellow, oxygen: blue). This amphiphilic octasulfonate anion exemplifies the first water‐soluble carboracycle. The hydrophobic cavity in the cycle is clearly viable and adjustable by inter‐cage linker modification. The development of new supramolecular chemistry and its use in molecular recognition employing solvent systems that range from organic to aqueous represent future applications of these novel carboracycle derivatives. For more details concerning the synthesis and characterization of these multifunctionalized carborane‐based macrocycles see the article by M. F. Hawthorne et al. on p. 2732 ff.
Vom einfachen Komplex zum komplexen Gitter: Metallo‐supramolekulare Chemie
Authors: Schmatloch Stefan , Schubert Ulrich S. 
Published: June 2003

AbstractKoordinationsverbindungen, die bereits im vorletzten Jahrhundert durch die klassische Komplexchemie und Koordinationslehre beschrieben wurden und seit den späten 50iger Jahren intensiv auf dem Gebiet der homogenen und heterogenen Katalyse Einsatz finden, stehen erneut im Mittelpunkt eines neuen Forschungsbereichs: der metallo‐supramolekularen Chemie. Komplizierte, supramolekulare Liganden, als Weiterentwicklung einfacher einzähniger Liganden und Chelatliganden, führen auf der Basis von Selbstorganisations‐ und Selbsterkennungsprozessen zusammen mit koordinierenden Metallionen zu genau definierten supramolekularen Architekturen. Die Natur nutzt diese als wesentliche Funktionsträger in biologischen Systemen, z. B. den Hämoglobin‐Eisen‐Komplex. Diesem Vorbild folgend versucht die supramolekulare Chemie, hochkomplexe, jedoch genau definierte Geometrien, wie Helikate, Fäden, Leitern, Rechen oder Gitter präparativ herzustellen und somit neuartige Materialien mit speziellen Eigenschaften zu entwickeln. Der Metallkomplex als zentrale Einheit der neuen Verbindungsklasse kann zu „funktionalen supramolekularen Systemen”︁ führen. Diese könnten Anwendungen auf den Gebieten der Polyelektrolyte, der Elektrochemie (elektrisch leitende Polymere und Redoxkatalysatoren) und der Photochemie (organische Solarzellen) ermöglichen.
Die Herstellung von Reinstsiliciumscheiben: Mehr Chemie als man glaubt
Authors: Wenski Guido , Hohl Georg , Storck Peter , Crößmann Ivo 
Published: June 2003

AbstractEinkristalline Halbleiterscheiben aus Silicium stellen die Grundlage für mikroelektronische Bauelemente dar. Die Umwandlung des Ausgangsmaterials Quarz in eine epitaktisch beschichtete 300‐mm‐Scheibe umfasst eine Vielzahl von Prozessschritten, die teilweise deutlich von chemischen Verfahren geprägt sind. Der vorliegende Aufsatz führt in die Herstellung von Halbleitersilicium sowie die Verfahren Ätzen, Polieren, Reinigen und Epitaxie ein. Was diesen Technologiezweig auszeichnet, sind die extremen Anforderungen an Oberfächenperfektion und Reinheit, die sich in Atomlagen (Oberflächenrauheit der Scheiben) und parts per trillion (Kontamination der Chemikalien) ausdrücken lassen.
Characterization of paraffin oils and petrolatum using LDI‐TOF MS and principle component analysis
Authors: Prunsa Julia K. , Rapp Claudius , Hintze Ulrich , Wittern Klaus‐Peter , König Wilfried A. 
Published: June 2003

AbstractLaser desorption/ionization time‐of‐flight mass spectrometry (LDI‐TOF MS) followed by evaluation of the mass spectra with principal component analysis (PCA) was used for the in‐depth characterization of paraffin oils (mineral oils) and petrolatum (paraffin jelly) samples. These raw materials are liquid and semisolid mixtures of hydrocarbons obtained from petroleum. Mass spectrometric analysis was done using a solvent‐free sample preparation with silver trifluoroacetate. The analysis was carried out on a commercially available matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometer.Mass spectra were evaluated using parameters calculated from the areas of different alkane and cycloalkane species and by PCA. The ratios between specific peak areas were chosen as PCA‐input data instead of the less reproducible absolute peak areas.The principal components enable comparison of a large number of samples and can also be used for visualization of data. In this work, it is clearly demonstrated that combining LDI‐TOF MS and PCA provides a fast and efficient tool for the characterization of paraffin oils and petrolatum. Petrolatum and four different kinds of paraffin oil were analyzed and the results compared with other analytical methods.
Synthesis and Properties of Oligodeoxynucleotides Possessing N‐Phosphoryl Groups
Authors: Moriguchi Tomohisa , Wada Takeshi , Sekine Mitsuo 
Published: June 2003

AbstractThis paper deals with the synthesis and properties of oligodeoxynucleotides of a Dickerson−Drew sequence, d(CGCGAATTCGCG), in which one of the four cytosine bases has been replaced with an N‐phosphorylated or N‐diethylphosphorylated cytosine base in order to study the effect of the N‐phosphoryl or N‐diethoxyphosphoryl group on their structural property and hybridization affinity. The CD spectra of these self‐complementary duplexes showed the typical B DNA‐type shape with very minor changes. In contrast, it was found from Tm experiments that N‐phosphoryl groups destabilized the DNA duplexes significantly through steric hindrance and electronic repulsion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Study of the Reactions between Vinylmagnesium Bromide and Imines Derived from (R)‐Glyceraldehyde − The Key Step in the Stereodivergent Synthesis of Conveniently Protected, Enantiopure syn‐ and anti‐2‐Amino‐1,3,4‐butanetriol Derivatives
Authors: Badorrey Ramón , Cativiela Carlos , Díaz‐de‐Villegas Maria D. , Díez Roberto , Gálvez José A. 
Published: June 2003

AbstractA total stereodivergent method for the synthesis of enantiopure syn‐ and anti‐2‐amino‐1,3,4‐butanetriol (ABT) derivatives from inexpensive and readily available D‐mannitol has been developed. Key steps include: (a) the diastereoselective addition of vinylmagnesium bromide to conveniently protected N‐benzylimines derived from (R)‐glyceraldehyde, and (b) the oxidative degradation of the C−C double bond of the resultant syn‐ and anti‐vinylaminodiol derivatives. The addition of vinylmagnesium bromide in diethyl ether to the N‐benzylimine derived from (R)‐2,3‐O‐isopropylideneglyceraldehyde affords the anti‐vinylaminodiol derivative, while the reaction with the N‐benzylimine derived from (R)‐2,3‐di‐O‐benzylglyceraldehyde affords the syn‐vinylaminodiol derivative, both with excellent diastereoselectivities (de > 98/2). Moreover, a reversal of the stereochemical course of the reaction is produced when (R)‐2,3‐O‐isopropylideneglyceraldehyde N‐benzylimine is precomplexed with ZnI2, in this case yielding the syn addition adduct as the major compound. Different reaction conditions (reagent molar ratio, reaction temperature) have been tested in order to determine their influences on the observed yields and diastereoselectivities. From the results of this study and a subsequent crossover experiment, some interesting mechanistic considerations can be inferred. Enantiopure anti‐ and syn‐vinylaminodiol adducts have been successfully converted into conveniently protected anti‐ and syn‐2‐amino‐1,3,4‐butanetriol (ABT) derivatives, key building blocks in the asymmetric synthesis of biologically active compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
New, Regioselective, One‐Pot Synthesis of (all‐E)‐Retinoic Acid and Analogues from Enaminodiester Synthons
Authors: Cartier Dominique , Valla Alain , Guillou Régis Le , Labia Roger , Potier Pierre 
Published: June 2003

AbstractA one‐pot synthesis of (all‐E)‐retinoic acid and related compounds from new enamino diester synthons is described. The enamino diesters was produced nearly quantitatively from methyl propylidene‐ and isopropylidenemalonate and DMF−DMA. This easy process allowed retinoic acid to be produced in 1 d and appeared advantageous to current industrial syntheses. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Structural Analysis of Cyclic Oligomers Consisting of Furanoid and Pyranoid ϵ‐Sugar Amino Acids
Authors: Well Renate M. van , Marinelli Luciana , Erkelens Kees , Marel Gijsbert A. van der , Lavecchia Antonio , Overkleeft Herman S. , Boom Jacques H. van , Kessler Horst , Overhand Mark 
Published: June 2003

AbstractCyclic oligomers composed of amide‐linked furanoid (i.e., 1, 3) and pyranoid (i.e., 2, 4) ϵ‐sugar amino acids (SAAs) were prepared by a cyclization/cleavage approach with use of the oxime resin. These cyclic homooligomers were constructed by use of the known N‐Boc protected furanoid ϵ‐SAA 11 and the novel pyranoid hydroxymethylene homologue 22. Conformational analysis of cyclic trimer 1 by an unrestrained simulated annealing technique showed that the furanoid rings of the residues I flip between a twist (north, P = 0°) and an envelope (south, P = 167°) conformation. Furthermore, the side chains connecting the carbonyl functionality (i.e. C2) proved to be rigid, while the other side chains (C7) are conformationally flexible. Similar conformational behaviour is observed for the side chains of the pyranoid ϵ‐SAA II residues in trimer 2, but the pyranoid ring chair conformation remains stable during the calculation. These conformational details may have important implications in the future design of SAA‐based artificial receptors or peptidomimetics. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Construction of Spiro[pyrrolidine‐3,3′‐oxindoles] − Recent Applications to the Synthesis of Oxindole Alkaloids
Authors: Marti Christiane , Carreira Erick M. 
Published: June 2003

AbstractThe spiro[pyrrolidine‐3,3′‐oxindole] ring system is found at the core of a number of alkaloids, which possess significant biological activity and are interesting, challenging targets for chemical synthesis. In the present review, we report on the different strategies for the synthesis of the spiro[pyrrolidine‐3,3′‐oxindole] ring system in the context of recent synthesis of coerulescine, horsfiline, elacomine, salacin, pteropodine, alstonisine, spirotryprostatin A and B, and strychnofoline. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Development of a Practical Total Synthesis of Discodermolide, a Promising Microtubule‐Stabilizing Anticancer Agent
Authors: Paterson Ian , Florence Gordon J. 
Published: June 2003

AbstractMarine organisms provide an important source of natural product diversity with an associated range of significant biological activities. Discodermolide, isolated in microscopic quantities from a deep‐water sponge, shares the same microtubule‐stabilizing mechanism as Taxol and has a promising antitumor profile. There is, however, a chronic supply problem hampering clinical development and so a practical total synthesis of discodermolide is an important goal. This review highlights the completed total syntheses of discodermolide, focusing on the various methods and strategies employed for achieving stereocontrol and realising the pivotal fragment couplings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Mucochloric Acid: A Useful Synthon for the Selective Synthesis of 4‐Aryl‐3‐chloro‐2(5H)‐furanones, (Z)‐4‐Aryl‐5‐[1‐(aryl)methylidene]‐3‐chloro‐2(5H)‐furanones and 3,4‐Diaryl‐2(5H)‐furanones
Authors: Bellina Fabio , Anselmi Chiara , Martina Francesca , Rossi Renzo 
Published: June 2003

Abstract3,4‐Dichloro‐2(5H)‐furanone, which has been prepared efficiently from mucochloric acid, has been transformed selectively into 4‐aryl‐3‐chloro‐2(5H)‐furanones either by Suzuki‐ or Stille‐type reactions. These monochloro derivatives have been used as precursors either to (Z)‐4‐aryl‐5‐[1‐(aryl)methylidene]‐3‐chloro‐2(5H)‐furanones, including naturally occurring rubrolide M, or to unsymmetrical 3,4‐diaryl‐2(5H)‐furanones. Some 2(5H)‐furanone derivatives so prepared have been found to exhibit significant cytotoxic activity in vitro against the NCI three‐cell‐line panel, but limited cytotoxicity against the NCI human tumor 60 cell‐line panel. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Shake table tests on a mass eccentric model with base isolation
Authors: Samali Bijan , Wu Yi Min , Li Jianchun 
Published: June 2003

AbstractA mass eccentric structure is usually more seismically vulnerable than its concentric counterpart because of the coupled torsional–translational response of such structures. In this work, dynamic characteristics and response of a five‐storey benchmark model with moderate mass eccentricity were investigated using a shake table, simulating four different ground motions. The effectiveness of laminated rubber bearings (LRB) and lead‐core rubber bearings (LCRB) in protecting eccentric structures was examined and evaluated in relation to translational and torsional responses of the benchmark model. It was observed that both translational and torsional responses were significantly reduced with the addition of either a LRB or LCRB isolated system regardless of the nature of ground motion input. The LRB were identified to be more effective than LCRB in reducing model relative displacements, the relative torsional angle as well as accelerations, and therefore provided a better protection of the superstructure and its contents. On the other hand, LCRB rendered a smaller torsional angle and absolute displacement of the base isolation system, hence a more stable structural system. Copyright © 2003 John Wiley & Sons, Ltd.