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  • 1
    Electronic Resource
    Electronic Resource
    A Methylene-Bridged Dialuminium Compound as a Chelating Lewis Acid: Complexation of Nitrite and Nitrate Anions by R2Al-CH2-AlR2[R = CH(SiMe3)2]⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 921-926 
    Details
    ISSN: 1434-1948
    Keywords: Aluminium ; Chelates ; Lewis acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sodium nitrite (NaNO2) dissolves readily in THF, when the methylene-bridged dialuminium compound R2Al-CH2-AlR2 [R = CH(SiMe3)2] 1 with two coordinatively unsaturated aluminium atoms is added. Compound 1 reacts as a chelating Lewis acid, and, as shown by a crystal structure deter-mination of the [Na([18]crown-6)(Et2O)]+ derivative 5c, a compound (5) is formed, in which one oxygen atom and the nitrogen atom of the nitrite ion are each coordinated by one aluminium atom to form a five-membered Al2CNO hetero-cycle. The second oxygen atom of the nitrite anion is not affected. Similarly, lithium nitrate (LiNO3) reacts with 1 to yield a THF soluble product (6a). Single crystals were obtain-ed of the [Li(N,N′,N′′-trimethyltriazinane)2]+ derivative 6c, whose structure shows each aluminium atom to be coordinated by one oxygen atom of the nitrate ion to give a six-membered Al2CNO2 heterocycle.
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  • 2
    Electronic Resource
    Electronic Resource
    Regioselective and Stereoselective Transformations of Enantiopure p-Benzoquinone Equivalents (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 643-650 
    Details
    ISSN: 1434-193X
    Keywords: Cycloaddition ; High pressure chemistry ; Quinones ; Cyclohexanones ; Retro Diels-Alder process ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The selectivities of typical transformations of the p-benzoquinone Diels-Alder adduct 2 and its dihydro derivative 3 are shown to be highly dependent on the mechanistic path followed. To avoid ambiguities and to make sure of clearly defined regioselectivity, the monoketal 13 was examined and proven not only to be an excellent dienophile but, of course, also to lead to reliable regioselectivity in subsequent transformations. This led to the correction of an earlier provisional assignment of the alkylation products 11 and 12.
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  • 3
    Electronic Resource
    Electronic Resource
    Cyclization of 3-Aminoacrylates - Total Synthesis of Pumiliotoxin C and Related Stereoisomeric Compounds (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2641-2646 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Total synthesis/Pumiliotoxin ; PTX-C ; PTX isomers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the synthesis of pumiliotoxin C (1a) and related stereoisomeric compounds 1c-1f. Starting from (+)- or (-)-3-methylcyclohexanone (6a,b), the oxo esters 7a and 7b were prepared. Condensation with (+)- or (-)-3-aminohexanol (8a,b) gave the stereoisomeric 3-aminoacrylates 9a, 9b and 9c. The hydroxy group of the amino-acrylates was transformed into bromide using the tosylate method. Cyclization of the bromides led to unsaturated quinoline ring systems. Finally, decarboxylation and catalytic hydrogenation gave the different cis- and trans-fused stereoisomeric alkaloids of the pumiliotoxin C type. The structures were verified by X-ray analysis.
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  • 4
    Electronic Resource
    Electronic Resource
    Addition and Ring Expansion Reactions of Tricarbonyl(1,2-dioxobenzocyclobutene)chromium(0) with Carbon Nucleophiles - Unexpected Formation of Benzocycloheptene Derivatives and the First Head-to-Head Coupling of Two Methoxyallene Molecules (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2719-2727 
    Details
    ISSN: 1434-193X
    Keywords: Chromium ; Benzocyclobutene ; Dianionic Oxy-Cope Rearrangement ; Methoxyallene ; Benzocycloheptenedione ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition of carbon nucleophiles to (benzocyclobutenedione)tricarbonylchromium(0) (4) results in the formation of exo mono- and diadducts as well as 1,2-diketones as the consequence of proximal ring-opening reactions. In one case the unexpected formation of benzocycloheptenedione complexes is observed. Treatment of 4 with an excess of 1-ethoxy-1-lithioethene gives the product of a dianionic oxy-Cope rearrangement followed by an intramolecular aldol addition. This is also the case with lithiated methoxyallene, and as the result the first head-to-head coupling product 12 of two methoxyallene molecules is isolated in good yield. 12 is used as a diene in Diels-Alder cycloadditions, and its molecular structure is compared to that of the similar molecule 13, lacking the two exo methylene substitutents.
    Additional Material: 2 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis, Characterization, and Some Reactions of the Tricarbonylchromium Complexes of 1,3-Indandione and Ninhydrin (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 167-179 
    Details
    ISSN: 1434-193X
    Keywords: 1,3-Indandione ; Ninhydrin ; Chromium complexes ; Acetals ; Oxidation ; Hetero Diels-Alder reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The syntheses and characterization of the tricarbonylchromium complexes of 1,3-indandione and ninhydrin are described. As the direct complexation proved unsuccessful, the acetal route was tried. Although some complexes were obtained, complex deacetalization did not work in the case of ninhydrin. Finally, the oxidation of tricarbonyl(η6-1,3-indandione)chromium(0) with dimethyldioxirane gave the ninhydrin complex in 75% yield in equilibrium with the indantrione complex. The latter reacts in hetero Diels-Alder reactions with dienes with diastereoselective formation of spiro anellated pyran derivatives.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Diastereoselective Ring Expansion Rearrangements of (Benzocyclobutenone)-and (Benzocyclobutenedione)chromium Complexes: Syntheses of Substituted 1-Indanone and 1,3-Indandione Complexes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 823-835 
    Details
    ISSN: 1434-193X
    Keywords: (Arene)chromium complexes ; α-Ketol rearrangement ; Vinylcyclobutene-cyclohexadiene rearrangement ; Benzocyclobutenes ; Indanone derivatives ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Organolithium and Grignard reagents add to the oxo group of (benzocyclobutenone)tricarbonylchromium(0) (1) diastereoselectively from the exo face of the organic ligand. If acyl anion equivalents are used as nucleophiles, deprotection of the carbonyl functions of the adducts causes ring expansion reactions to occur. Among these a rare example of an anion-accelerated 1-vinylcyclobutenol-cyclohexadienol rearrangement is reported which results, after isomerization, in a naphthol complex. Other ring expansion reactions gave coordinated substituted indanone derivatives. The facial differentiation by the tricarbonylchromium moiety allows for the first time the determination of the distereoselectivity of these reactions. The 1-oxoindan-2-ol derivatives obtained can undergo an α-ketol rearrangement with formation of the corresponding 2-oxoindan-1-ol complexes. Some of these reactions were performed with nonracemic starting material in order to determine how far chirality transfer from the planar chiral starting material to C-2 in the indanone system was possible. The ring expansion was also feasible with the benzocyclobutenedione complex as a starting compound, the reaction giving substituted 1,3-indandione complexes. Crystal structure analyses of three of the complexes prepared are reported.
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Benzil Derivatives as Trapping Reagents for the Monomeric Alkylindium(i) Compound in-c(SiMe3)3 (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1269-1272 
    Details
    ISSN: 0009-2940
    Keywords: Indium ; Clusters ; Low-valent compounds ; Trapping reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrahedral cluster compound tetrakis[[Tris(trimethylsilyl)methyl]indium(I)] 91) reacts in boiling n-hexane with benzil derivatives (p-X-C6H4)C(O)(p-X-C6H4) (X = H, OMe, Br), to yield the 1,4-cycloadditon products of the monomeric alkylindium(I), In-C(SiMe3)3, in which the In atoms are coordinated by a chelating enediolato ligand, to form a five-membered InO2C2 heterocycle. As shown by two crystal structure determinations (X = H, OMe), the products are dimeric in the solid state, with a four-membered In2O2 heterocycle in the molecular center and both C(SiMe3)3 groups, as well as both enediolato substitutents in a cis arrangement.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300915
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis and reactions of novel tricyclo[4.3.1.12,5]undec-3-en-10-ones (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2131-2139 
    Details
    ISSN: 0009-2940
    Keywords: Stereoselective synthesis ; Rings, bridged seven-membered ; Ketones, α,α'-dibromo, monoterpenoid ; Oxyallyl cations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sodium iodide/copper mediated intermolecular cyclodehalo-genation of 2,6-dibromocyclohexanones in the presence of furan and cyclopentadiene afforded a variety of alkylated tricyclo[4.3.1.12,5]undec-3-en-10-ones. An alkyl group (methyl or isopropyl) adjacent to the carbonyl carbon atom in the starting 2,6-dibromocyclohexanone derivative was important for the success of the cycloaddition procedure. Even tricylic ketone 11, containing two quaternary carbon atoms adjacent to the carbonyl carbon atom, was prepared. The α,α'-dibromoketones derived from either enantiomer of menthone and cyclopentadiene reacted enantioselectively, yielding tricycles (7R)-7 and (7S)-7. Since a number of tricyclic ketones 3-11 were sensitive, they were reduced to secondary alcohols 19-25, having an axial, α-configurated OH group and were also converted into tertiary methylcarbinols 26 and 27 using methyllithium activated with tBuOK. Secondary α-configurated alcohols 19-25 had an earthy-mouldy odour, and tertiary carbinols 26 and 27 even more so. Unsaturated alcohols 26 and 27 showed a 4 J coupling of 2 Hz between the rigidly held OH proton and the nearest methyl protons. On hydrogenation of the olefinic double bond (4 → 33, → 34) this long-range coupling disappeared.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231108
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  • 9
    Electronic Resource
    Electronic Resource
    Diazomethane Derivatives Bearing Dialkylaluminium or DialkylgalliumSubstituents - The Isomeric Diazomethane and Nitrile Imine Structures Realized by the Different Coordination Behavior of Aluminium and Gallium (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 771-776 
    Details
    ISSN: 1434-1948
    Keywords: Aluminium ; Gallium ; Diazo compounds ; Dimerization ; Coordination modes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithium trimethylsilyldiazomethanide Li(SiMe3)CN2 reacted with the dialkylaluminium or -gallium halides R2AlCl and R2GaBr [R = CH(SiMe3)2] by the elimination of lithium halide and the formation of the corresponding aluminium or gallium diazo compounds. As shown by a crystal structure determination, the gallium derivative 1 adopts the nitrile imine structure, in which the gallium atom is coordinated by the terminal nitrogen atom of the diazo group. The N-N-C-Si moiety is almost ideally linear with N-N and C-N bond lengths of 125.5 and 115.9 pm on average. In contrast, the diazomethane structure was formed with dialkylaluminium chloride, and the aluminium atom in 2 is attached to the carbon atom of diazomethane. The almost linear N-N-C group (174.1°) has N-N and N-C distances of 120.0 and 126.4 pm, respectively, inverse to that of the gallium derivative. The bonding situations can best be described by the resonance structures R-C≡N+-N--GaR2 for 1 and R2Al-(R)C=N+=N- for 2. The nitrile imine isomer of the aluminium compound could be detected by NMR spectroscopy as a by-product. Both compounds gave dimers in the solid state, a Ga2N2 four-membered heterocycle was formed of 1, while an eight-membered Al2C2N4 heterocycle resulted with 2.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Stereokontrollierte Konstruktion von 6·5·6- und 5·5·6-Ringsystemen durch radikalische Tandem-CyclisierungDiese Arbeit wurde vom Fonds der Chemischen Industrie gefördert. U. Eggert danken wir für experimentelle Beiträge.Professor Ekkehard Winterfeldt zum 60. Geburtstag gewidmet (1992)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 104 (1992), S. 903-906 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19921040730
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