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  • 11
    Electronic Resource
    Electronic Resource
    C—C Bond Formation via Carbon-Centered Radicals Generated from Dicarbonyl(η5-cyclopentadienyl) organoiron Complexes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1143-1155 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of benzyldicarbonyl(η5-cyclopentadienyl)iron complex (2) leads to hemolytic cleavage of the Fe—C bond. In the presence of activated alkenes, radical addition occurs and both saturated and unsaturated addition products 7-9 are formed. Photolysis of alkyliron complexes 2,3 and 20 in the presence of acrylonitrile leads to the same products as the irradiation of the respective acyliron complexes 28-30. This indicates that, under photolytical conditions, alkyl and acyl complexes are in equilibrium with each other.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740524
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  • 12
    Electronic Resource
    Electronic Resource
    Dimeric Metal Complexes as Mediators for Radical C—C Bond-Forming Reactions (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1135-1142 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of dicarbonyl(η5-cyclopentadienyl)iron dimer 1 or decacarbonyldimanganese (2) in the presence of alkyl halides leads to C-centered radicals which can be trappedby alkenes and yields saturated and/or unsaturated addition products. Carbon radicals are generated via halogen abstraction by the initially formed metal-centered radicals resulting from homolysis of the metal-metal bond of dimeric mediators 1 and 2. No reaction occurs using octacarbonyldicobalt (3).
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740523
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  • 13
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis of 3-Hydroxyprolines by Photocyclization of N-(2-Benzoylethyl)glycinamidesDedicated to Professor Dr. Hans-Georg Henning on the occasion of his 65th birthday (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 829-837 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral N-(2-benzoylethyl)-N-tosylglycinamides 1a-c were prepared from the C2-symmetric pyrrolidines 5a-c. Irradiation of these ketones 1a-c gave cis-3-hydroxyprolinamides 10-12 in moderate to good yields (Scheme 3). The de of the photocyclizations depended on the size of the substituents in positions C(2) and C(5) of the chiral pyrrolidine auxiliaries. In addition, the de varied with the reaction temperature, allowing the determination of activation-parameter differences. The structure of products 10-12 were established by NMR and X-ray analyses.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770322
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  • 14
    Electronic Resource
    Electronic Resource
    Efficient Control of the Stereoselectivity in Reactions of 2-Oxy-Substituted Benzylic Radicals (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1006-1012 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselectivity in reactions of 2-oxy-substituted radicals of type B was investigated. As expected, minimization of allylic 1,3-strain was the major controlling factor. Under standard conditions, only a modest level of stereoselectivity was observed. E.g., deuteration of the benzylated radical (R1 = benzyl) gave diastereoisomer ratios ≤ 2:1. Use of a bulky protective group on the O-atom (R1 = (t-Bu)Ph2Si) enhanced slightly the selectivity (ratio 4.1:1). However, a dramatic increase of the stereoselectivity (ratio 13:1) was obtained, when the reaction was performed with the free alcohol after treatment with bulky methylaluminium bis(phenoxide) derivatives (methyl-aluminium bis[2,6-di(tert-butyl)-4-methylphenoxide] (MAD) and methylaluminium bis(2,6-diphenylphenoxide) (MAPH)).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780422
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  • 15
    Electronic Resource
    Electronic Resource
    Synthesis of 4′-C-Acylated Thymidines (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1980-1994 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two synthetic pathways towards 4′-C-acylthymidines are presented. These modified mononucleosides are precursors of the 2′-deoxyribonucleotide 4′-C-radical. They were converted into their corresponding 3′-O-[(2-cyanoethyl) N,N-diisopropylphosphoramidites] 3a-c and incorporated in oligonucleotides by solid-phase synthesis. The structure of some modified nucleosides was revealed by X-ray crystal-structure analysis.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790720
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  • 16
    Electronic Resource
    Electronic Resource
    Photolytic Reactions of (o-Allylbenzyl)dicarbonyl(η5-cyclopentadienyl)iron (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 1123-1129 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photolysis of (o-allylbenzyl)dicarbonyl(η5-cyclopentadienyl)iron (4) at 20° in CH2Cl2 leads to carbon-monoxide loss followed by intramolecular complexation to [η2-(o-allylbenzyl)]carbonyl(η5-cyclopentadienyl)iron (13). At 50° in C6D6, a photochemical rearrangement proceeds forming carbonyl (η5-cyclopentadienyl){η3-[3-(2-methylphenyl)allyl]}iron (17). Depending on the temperature, photolysis of 4 leads to intermolecular reactions at the benzylic or allylic position of the π complexes 13 and 17, respectively.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750415
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  • 17
    Electronic Resource
    Electronic Resource
    Einfluß der Substituenten auf Aktivierungsenthalpie-,-entropie und -volumen beim Zerfall organischer Perester (1985)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 240-245 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Influence of Substituents on the Enthalpy, Entropy and Volume of Activation in the Decomposition of Organic PerestersThe influence of the ester group on the decomposition of organic peroxides was studied on peresters of the pivalic and neodecanoic acid with tert-butyl, tert-amyl, 1-methyl-1-propylpentyl and 1,1,4-trimethylpentyl groups at temperatures of 393 to 473 K and pressures up to 3000 bar using a flow method. As expected the half-live times decrease with increasing temperature and increase with rising pressure. With increasing bulkiness of the substituents the rates of decomposition as well as the enthalpies of activation increase. This surprising fact can be explained by the simultaneous increase of the entropies and the volumes of activation.
    Notes: Der Einfluß der Estergruppe auf den Zerfall organischer Peroxide wurde an Perestern der Pivalin- und der Neodecansäure mit tert-Butyl-, tert-Amyl-, 1-Methyl-propylpentyl- sowie 1,1,4-Trimethylpentylresten bei Temperaturen von 393 bis 473 K und Drücken bis 3000 bar in einer Strömungsapparatur untersucht. Die Zerfallshalbwertszeiten nehmen erwartungsgemäß mit steigender Temperatur stark ab und mit steigendem Druck zu. Mit zunehmender Größe der Substituenten steigen sowohl die Zerfallsgeschwindigkeiten als auch die Aktivierungsenthalpien. Dieser überraschende Effekt kann durch die Vergrößerung der Aktivierungsentropie und des Aktivierungsvolumens erklärt werden.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19851180123
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  • 18
    Electronic Resource
    Electronic Resource
    Notizen.Bestimmung absoluter Geschwindigkeitskonstanten bei der radikalischen Addition an Alkene nach der “Quecksilbermethode” (1984)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 117 (1984), S. 3160-3164 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurement of Absolute Rates of Radical Additions to Alkenes by the “Mercury Method”Using the 5-hexenyl radical (2) as “radical clock” the rates of radical additions to methyl acrylate (5a) and acrylonitrile (5b) are measured by the “mercury method” (Table 1). Alkyl radicals are trapped by the alkylmercury hydride 1 with rate constants of at least 107 1 · mol-1 · s-1.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19841171015
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  • 19
    Electronic Resource
    Electronic Resource
    Radikalkettenreaktionen mit Maleinsäureanhydriden  -  Zur kontrathermodynamischen Stereoselektivität (1984)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 117 (1984), S. 3175-3182 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Radical Chain Reactions with Maleic Anhydrides  -  Contrathermodynamic StereoselectivityThe reactions of cyclohexylmercuric chloride with NaBH4 and alkenes 1a-g yield 60-84% of products 3, 4 and 6 in a radical chain process (table 1). Caused by steric effects of substituents Z at least 97% of the radical attack occurs at the unsubstituted carbon atom of maleic anhydrides 1c-g. Only fluoromaleic anhydride 1b is attacked by cyclohexyl radicals predominantly at the substituted carbon atom, because fluorine is a tiny, electron releasing substituent. Radicals 2 are trapped predominantly from the anti-direction by the H-donor (figure 1), yielding cis-compounds 3 as main products. This „contrathermodynamic“ stereoselectivity ranges between 2.3 and 19 (table 1).
    Notes: Die Reaktion von Cyclohexylquecksilberchlorid mit NaBH4 und den Alkenen 1a-g liefert in einer Radikalkettenreaktion die Produkte 3, 4 und 6 in 60- bis 84proz. Ausbeuten (s. Tab. 1). Wegen der sterischen Effekte der Substituenten Z erfolgt der Angriff der Radikale zu mindestens 97% am unsubstituierten C-Atom der Maleinsäureanhydride 1c-g. Allein das Fluormaleinsäureanhydrid 1b wird bevorzugt am substituierten C-Atom durch Cyclohexyl-Radikale angegriffen. Die Ursache für diese umgekehrte Regioselektivität liegt in der geringen Raumerfüllung und dem elektronenspendenden Effekt des Fluoratoms. Die H-Übertragung auf die Radikale 2 erfolgt überwiegend von der anti-Seite (s. Abb. 1), so daß die thermodynamisch instabileren cis-Verbindungen 3 als Hauptprodukte entstehen. Diese „kontrathermodynamische“ Stereoselektivität liegt zwischen 2.3 und 19 (s. Tab. 1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19841171103
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  • 20
    Electronic Resource
    Electronic Resource
    Experimental and theoretical studies on the mechanism of 1,2-migration of vinyl and formyl substituents in free radicals (1986)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 3528-3535 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Experimentelle und theoretische Untersuchungen zum Mechanismus der radikalischen 1,2-Umlagerung von Vinyl- und FormylgruppenDie Umlagerungen von Vinyl- und Formylgruppen vom Typ X=CH — CMe2 — ĊH2 → ĊMe2 — CH2 — CH=X (X=CH2 oder O) erfolgen mit vergleichbaren Geschwindigkeiten (106 - 107 l/mol · s, 20°C). In Übereinstimmung mit diesen kinetischen Messungen stehen ab-initio-Rechnungen, nach denen für die Grundkörper Aktivierungsenergien von 14.9 (CH2=CH — CH2 — CH2) und 19.2 kcal/mol (O=CH — CH2 — ĊH2) berechnet werden. Die Rechnungen sagen Cyclopropanderivate als Zwischenstufen der Umlagerung voraus.
    Notes: Vinyl and formyl groups undergo rearrangements of the type X=CH — CMe2 — ĊH2 → ĊMe2 — CH2 — CH=X (X=CH2 or O) with comparable rates (106 — 107 l/mol · s, 20°C). This result is in line with high-level ab initio calculations performed on the basic systems, i.e. X=CH — CH2 — ĊH2, which give barriers of activation of 14.9 (CH2=CH — CH2 — ĊH2) and 19.2 kcal/mol (O=CH — CH2 — ĊH2), respectively. The calculations suggest that the rearrangements proceed via cyclopropane-like intermediates.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19861191203
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