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  • 1
    Electronic Resource
    Electronic Resource
    Diastereomerically Pure 1,2-Diols by Nucleophilic Displacement Reactions of 3-Oxetanols - A Study Directed Towards the Identification of Suitable Nucleophiles and the Elucidation of Possible Side Reactions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2161-2169 
    Details
    ISSN: 1434-193X
    Keywords: Photocycloaddition ; Ring opening ; Oxetanes ; 1,2-Diols ; Alkyldealkoxylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring opening of 3-isopropyl-2-phenyl-3-oxetanol (2a) by various nucleophiles has been studied. In the presence of BF3 as a Lewis acid, a clean reaction at the less substituted C-4 position was observed and the corresponding 1,2-diols 6-11 and 21-23 were isolated in diastereomerically pure form (47-97% yield). Alkyl-, aryl-, alkynyl- and alkenyllithium compounds proved to be suitable carbon nucleophiles. Deprotonated thiols were used as sulfur nucleophiles. An alkoxide derived from benzyl alcohol and an amide derived from benzylamine reacted less readily under these conditions, yielding the 1,2,3-trifunctional compounds 24 (42% yield) and 26 (54% yield). Other 2-phenyl-3-oxetanols such as 2b and 2c can also be employed as electrophiles, whereas 2-anisyl derivatives preferentially undergo rearrangement reactions, as exemplified by the conversion of oxetane 16 to the hydroxy ketone 17 (84% yield). The superior behaviour of 3-oxetanols as compared to their silyl derivatives in reactions with nucleophiles became evident from the reaction of 3-silyloxyoxetane 1a with alkyllithium reagents. A β elimination occurred upon treatment with nBuLi, which, after pericyclic ring opening and addition of nBuLi, yielded the allylic alcohol 20.
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  • 2
    Electronic Resource
    Electronic Resource
    The Preparation of 2,3,5-Tri- and 2,3-Disubstituted Furans by Regioselective Palladium(0)-Catalyzed Coupling Reactions: Application to the Syntheses of Rosefuran and the F5 Furan Fatty Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2045-2057 
    Details
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Palladium ; Cross-coupling ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5-acceptor-substituted 2,3-dibromofurans 1 and 2 underwent a regioselective Pd0-catalyzed coupling reaction at the C-2 carbon atom. With alkynes the corresponding 2-alkynylfurans 4 and 5 were accessible (49-97% yield). Alkyl-, aryl-, and alkenylzinc reagents gave the 2-substituted furans 8 starting from compound 2 (66-84% yield). The 2-allylfurans 8e and 8f were obtained by a regioselective Stille coupling in 79% and 73% yield. The latter reaction was also applied to the parent 2,3-dibromofuran (27) and yielded the substitution product 28 (60% yield). Subsequent Pd0-catalyzed reactions to introduce a methyl group in 3-position by a methyldebromination were successfully conducted for 2-alkynyl-3-bromofurans with MeZnCl and PdCl2(PPh3)2 as the catalyst in THF (reflux) to yield compounds 13-16 and 24 (67-76%) and with SnMe4 and PdCl2[P(o-Tol)3]2 as the catalyst in DMA (90 °C) for the 2-allyl-3-bromofuran 8e to yield 18 (70%). The more facile reaction of the 2-alkynylfurans relative to those of furans bearing an sp3-carbon atom at C-2 appears to be due to steric reasons. Studies on the 2-alkyl-3-bromofuran 20 supported this notion. With the regioselective coupling methodology the terpene rosefuran (22) was prepared in four steps starting from furan 2 (35% yield overall). The F5 furan fatty acid (26) was synthesized from furan 1 in five steps (29% yield overall).
    Additional Material: 4 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Control of the J-Aggregation Phenomenon by variation of the N-alkyl-substituents (1995)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 337 (1995), S. 203-208 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyanine dyes (1a-d) with the 5,5′,6,6′-tetrachloro-1,1′-dialkyl-3,3′-di-(3-carboxypropyl)-benzimidocarbocyanine chromophore differing only in the chain length of their alkyl groups in 1,1′-position have been synthesized, spectroscopically characterized, and compared with 5,5′6,6′-tetrachloro-1,1′-diethyl-3,3′-di-(4-sulfobutyl)-benzimidocarbocyanine(TDBC). In aqueous solution the dyes form J-aggregates which, depending on the alkyl group chain length, exhibit J-bands differing in spectral positions, bandwidth, and in the number of peaks.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19953370144
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  • 4
    Electronic Resource
    Electronic Resource
    Diastereomerically Pure 3-Alkoxy- and 3-Acyloxyoxetanes from 3-silyloxyoxetanes. A case study (1996)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 750-753 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.199633801146
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  • 5
    Electronic Resource
    Electronic Resource
    Regioselective ring opening of oxetanes by hydrogenolysis. - A convenient method for the carbohydroxylation of enol ethers (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1045-1053 
    Details
    ISSN: 0947-3440
    Keywords: Photocycloaddition ; Hydrogenolysis ; Oxetanes ; Carbohydroxylation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrogenolysis of the 2-aryl-3-(silyloxy)oxetanes 1, 2, 5, and 9 in the presence of Pd(0) catalysts (Pd/C) yields 1,2-diols as ring-opened products almost quantitatively (82-98% yield). In combination with the preceding photocycloaddition it facilitates the regio- and stereoselective carbohydroxylation of silyl enol ethers (total yield: 43-74%). In the case of β-substituted silyl enol ethers (R1 = alkyl) the reaction sequence leads to a single diastereomeric product (4, 6, 10) in a simple two-step procedure. Acid-sensitive substrates such as the dioxolane 1g or the dihydrofuran-derived oxetane 11 are mildly cleaved in the presence of Pd(OH)2. As demonstrated by selected examples (13, 16, 18) the produced 1,2-diol remains silyl-protected if Pd(OH)2 is employed as a catalyst for the hydrogenolysis. In the latter case the silyl protective group stays at the tertiary hydroxy group to which it has been attached in the oxetane, but silyl migration may intervene as was found in the case of the sterically congested oxetane 18.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199506148
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  • 6
    Electronic Resource
    Electronic Resource
    A Short Synthesis of (±)-Oxetin (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2265-2267 
    Details
    ISSN: 0947-3440
    Keywords: Antibiotics ; Amino acids ; Photochemistry ; Oxetanes ; Protective groups ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The antibiotic β-amino acid oxetin (rac-1) has been prepared by the stereoselective Paternò-Büchi reaction of enecarbamate 2 and n-butyl glyoxylate (5). The overall yield of the four-step synthesis is 14%. The order of the deprotection steps proved to be important in minimizing possible side reactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971113
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  • 7
    Electronic Resource
    Electronic Resource
    Erste Erfahrungen bei der Detektion von Rissen in Fernrohrleitungen mit Impuls-WirbelstromVortrag, gehalten auf dem Querschnittsseminar „Korrosionsüberwachung mit ZfP“ der DGZpf, Berlin, 28.-29. November 1994 (1995)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 46 (1995), S. 418-421 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: First experiences with the detection of cracks in long-distance onshore pipelines with the pulse-eddy current-techniqueLong-distance onshore pipelines are inspected for their reliability by means of so-called pigs. For checking pipelines for internal cracks, a pig based on a pulse eddy current technique has been developped. The structure of the pig, the eddy current technique and first measuring results as well as advantages and disadvantages are described in the following paper.
    Notes: Erdverlegte Fernrohrleitungen werden mit sogenannten Molchen auf deren Zuverlässigkeit untersucht. Für die Prüfung auf Innenrisse wurde ein Molch auf Impulswirbelstrombasis entwickelt. Der Aufbau des Molches, das verwendete Wirbelstromverfahren und erste Meßergebnisse werden beschrieben. Die Vor- und Nachteile werden aufgezeigt.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19950460707
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  • 8
    Electronic Resource
    Electronic Resource
    The Preparation of N-tert-Butyloxycarbonyl-(Boc-)Protected Sulfoximines and Sulfimines by an Iron(II)-Mediated Nitrene Transfer from BocN3 to Sulfoxides and Sulfides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1033-1039 
    Details
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Iron ; Imidation ; Sulfur ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The imidation of sulfides and sulfoxides to the corresponding sulfimides and sulfoximides was carried out with N-tert-butyloxycarbonyl azide (BocN3) in the presence of FeCl2. Sulfoxides 1 reacted at room temperature in CH2Cl2 to give the corresponding sulfoximides 3 in 40-95% yield. The imidation of the sterically congested substrate tert-butyl methyl sulfoxide (1f) proceeded sluggishly (10% yield). The sterospecificity of the reaction was demonstrated with the enantiomerically enriched substrates (R)-(+)-1b and (S)-(-)-1d which yielded the sulfoximides (R)-(+)-3b and (S)-(-)-3d with retention of configuration. Mechanistically, an intermediate (nitrene)FeIV complex is postulated as the reactive nitrene transfer reagent which is formed from FeCl2 and BocN3. The more nucleophilic sulfides 2 reacted more readily in the imidation than sulfoxides. Their conversion to the corresponding sulfimides 4 was conducted with BocN3 and a substoichiometric amount of FeCl2 (0.25 equiv.). Yields ranged between 44 and 92%. In an alternative reaction mode, BocN3 was utilized at 0°C in the presence of FeCl2 and acetyl acetone. The sulfimidation, which did not otherwise occur at this temperature, was accelerated by the ligand (36-90% yield).
    Additional Material: 4 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis of chemically bonded poly(vinyl alcohol)-starch compositeResults published in this paper were extracted from the Ph.D. Thesis to be submitted by M. M. Hashem to Cairo Univ./Egypt. (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 230 (1995), S. 189-204 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Zur Entwicklung neuartiger, ökologisch verträglicher makromolekularer Schlichtemittel wurden Copolymerisationsreaktionen zwischen Polyvinylalkohol (PVA) und Stärke unter Verwendung von chemisch reaktiven, bifunktionellen Verbindungen wie N-Methylolacrylamid (N-MAm) untersucht. Die Copolymerisationsreaktion wurde in zwei Schritten durchgeführt. Im ersten Reaktionsschritt erfolgt eine Additionsreaktion von N-MAm mit PVA unter alkalischen Bedingungen. Im Rahmen der Untersuchungen wurde der Einfluß verschiedener Reaktionsparameter wie Alkali-Konzentration, Temperatur, Reaktionszeit sowie der N-MAm-Konzentration geprüft. Die zweite Reaktionsstufe besteht in einer Pfropfcopolymerisationsreaktion von substituiertem Polyvinylalkohol (N-MAm-PVA) mit hydrolytisch abgebauter Stärke in Anwesenheit von NH4Cl. Auch hier wurde der Einfluß unterschiedlicher Reaktionsbedingungen wie Temperatur, Reaktionszeit sowie Konzentrationen der eingesetzten Katalysatoren und Reaktanden untersucht. Mit Hilfe der Gelpermeationschromatographie wurde nachgewiesen, daß die Molekulargewichtsverteilung und die Viskosität von PVA-Stärke-Copolymeren von den Molekulargewichten der Ausgangspolymeren (PVA, Stärke) abhängt.
    Notes: Poly(vinyl alcohol) (PVA) was grafted on hydrolysed starch through introduction of the chemically reactive bifunctional compound N-methylolacrylamid (N-MAm). The grafting reaction was carried out in two separate reaction steps. The first step was the reaction of PVA with N-MAm in alkaline medium. The reaction mechanism and reaction conditions such as alkali concentration, temperature, reaction time as well as N-MAm concentration were studied. According to the results obtained, the most appropriate conditions for the preparation of this reactive PVA are: treating PVA with N-MAm (1.25 mol/mol PVA) in the presence of NaOH (6% based on solution volume) at 20°C for 8 h. Second step was the reaction of this reactive PVA (N-MAm-PVA) with hydrolysed starch in the presence of NH4Cl. The latter was carried out under different conditions including temperature, reaction time, catalyst concentration as well as N-MAm-PVA/hydrolysed starch ratio. The results obtained show that the extent of the grafting reaction is governed by each of these factors. Furthermore, GPC data showed that the molecular weight distribution and the apparent viscosity of PVA-N-MAm-starch composite depend on the initial molecular weight of both PVA and hydrolysed starch used.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052300114
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  • 10
    Electronic Resource
    Electronic Resource
    The Paternò-Büchi Reaction of 3-Heteroatom-Substituted Alkenes as A Stereoselective Entry to Polyfunctional Cyclic and Acyclic MoleculesDedicated to Professor G. A. Olah on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1627-1634 
    Details
    ISSN: 0947-3440
    Keywords: Photochemistry ; Synthetic methods ; Oxetanes ; Diols ; Amino alcohols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of 3-heteroatom-substituted oxetanes by the Paternò-Büchi reaction, and their application in synthesis are reviewed. 3-Oxetanols and 3-aminooxetanes are the two most important oxetanes in this respect. By tuning the electronic properties of the enol and enamine substrates, a successful photocycloaddition to carbonyl compounds, with high yield, is possible. Since the oxetane formation proceeds stereoselectively, diastereomerically pure products are readily accessible, which can then be used in further transformations. To this end, regioselective ring-opening reactions have been developed, some of which will be discussed in this account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970803
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