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  • 1
    Electronic Resource
    Electronic Resource
    Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds part VIPart V: [1] Derivatives with Bidentate Ligands, Crystal Structures of tetrahedro- Decacarbonyl{μ-[1,1-bis(methylthio-χS)ethane]}tetrairidium ([Ir4(CO)10-(μ2-(MeS)2CHMe)]), tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{ethylidenebis- [diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-(Ph2P)2CHMe)]), and tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{propane-1,3-diylbis[diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-Ph2P(CH2)3PPh2)]) (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 781-791 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The disubstituted clusters[Ir4(CO)10(μ2-L—L)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (L—L = (MeS)2CHMe, cluster 1) or with three edge-bridging COs (L—L = (Ph2P)2CHMe, cluste 2; L—L =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C-NMR study of 1-3 shows that their respective ground-state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry-go-round of six COs about a unique trangular face and the rotation of terminal COs about one Ir-atom. The factors affecting the activation energy of the merry-go-round result from the relative bites of the bidentate ligands in the ground-state geometry, as shown by a comparison of the molecular structures of 2 and 3.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810328
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  • 2
    Electronic Resource
    Electronic Resource
    NMR of Enaminones. Part 7Part 6: [l]. The general name enaminone is used for compounds containing the O=C—C=C—N moiety. 1H-, 13C-, and 17O-NMR and X-ray structure determinations of 1,2-disubstituted conjugated 3-[(tert-Butyl)amino]enones (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2137-2147 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H-, 13C-, and 17O-NMR spectra for the 2-substituted enaminones MeC(O)C(Me)=CHNH(t-Bu) (1), EtC(O)C(Me)=CHNH(t-Bu) (2), PhC(O)C(Me)=CHNH(t-Bu) (3), and MeC(O)C(Me)=CHNH(t-Bu) (4) are reported. These data show that 3 exists mainly in the (E)-form, 4 in (Z)-form, and 1 and 2 as mixtures of both forms. Polar solvents favour the (E)-form. The (Z)- and (E)-forms exist in the 1,2-syn,3,N-anti and 1,2-anti,1,N-anti conformations A and B, respectively. The structures of the (E)- and (Z)-form are confirmed by X-ray crystal-structure determinations of 3 and 4. The shielding of the carbonyl O-atom in the 17O-NMR spectrum by intramolecular H-bonding (ΔλHB) ranging from -28 to -41 ppm, depends on the substituents at C(l) and C(2). Crystals of 3 at 90 K are monoclinic. with a = 9.618(2) Å, b = 15.792(3) Å, c = 16.705(3) Å, and β = 94.44(3)°, and the space group is P21/c with Z = 8 (refinement to R = 0.0701 on 3387 independent reflections). Crystals of 4 at 101 K are monoclinic, with a = 16.625(8) Å, b = 8.637(6) Å, c = 11.024(7) Å, and β = 101.60(5)°, and the space group is Cc with Z = 4 (refinement to R = 0.0595 on 2106 independent reflections).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800713
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  • 3
    Electronic Resource
    Electronic Resource
    Stereoselective Reactions of Phthalimido-Substituted Radicals Derived from (±)-Threonine: A comparison with reactions of N-phthaloyliminium ions (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 268-284 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective reactions of phthalimido-substituted radicals derived from (±)-threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N-phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin-Anh model (Fig. 3).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810208
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  • 4
    Electronic Resource
    Electronic Resource
    The Diels-Alder Reactivity of 2,2′-Ethylidenebis[3,5-dimethylfuran] and Exploratory Chemistry of the Mono-adducts (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1415-1427 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of Me3Al, 1-cyanovinyl acetate added to 2,2′-ethylidenebis[3,5-dimethylfuran] (1) to give a 20:10:1:1 mixture of mono-adducts 4,5,6, and 7 resulting from the same regiocontrol (‘para’ orienting effect of the 5-methyl substituent in 1). The additions of a second equiv. of dienophile to 4-7 were very slow reactions. The major mono-adducts 4 (solid) and 5 (liquid) have 2-exo-carbonitrile groups. The molecular structure of 4(1RS,1′RS,2SR,4SR)-2-exo-cyano-4-[1-(3,5-dimethylfuran-2-yl)ethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl acetate) was determined by X-ray single-crystal radiocrystallography. Mono-adducts 4 and 5 were saponified into the corresponding 7-oxanorbornenones 8 and 9 which were converted with high stereoselectivity into (1RS,1′SR,4RS,5RS,6RS)-4-[1-(3,5-dimethyl furan-2-yl)ethyl]-6-exo-methoxy-1,5-endo-dimethyl-7-oxabicyclo [2.2.1]heptan-2-one dimethyl acetal (12) and its (1′RS-stereoisomer 12a, respectively. Acetal hydrolysis of 12a followed by treatment with (t-Bu)Me2SiOSO2CF3 led to silylation and pinacol rearrangement with the formation of (1RS,1′RS,5RS,6RS)-4-[(tert-butyl)dimethy lsilyloxy]-1-(3,5-dimethylfuran-2-yl)ethyl]-5-methoxy-6-methyl-3-methylidene- 2-oxabicyclo[2.2.1]heptane (16). In the presence of Me3Al, dimethyl acetylenedicarboxylate added to 12 giving a major adduct 19 which was hydroborated and oxidized into (1RS,1′RS,2″RS,3″RS,4SR,4″RS,5 SR,6SR)-dimethyl 5-exo-hydroxy-4,6-endo-dimethyl-1-[1-(3-exo,5,5-trimeth oxy-2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-2-yl)ethyl]-7-oxabicyclo [2.2.1]hept-2-ene-2,3-dicarboxylate (20). Acetylation of alcohol 20 followed by C=C bond cleavage afforded (1′RS,1″SR,2RS,2′″SR,3RS, 3″SR,4RS,4″SR,5RS)-dimethyl {3-acetoxy-2,3,4,5-tetrahydro-2,4-dimethyl-5-[1-(3-exo,5,5-trimethoxy -2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-1-yl)-ethyl]furan-2,5-diyl} bis[glyoxylate] (24).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790514
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  • 5
    Electronic Resource
    Electronic Resource
    Hetero-Diels-Alder Additions of α,β-Unsaturated-Acyl Cyanides. Part 3Part 1: [7], part 2: [8].. Syntheses of 3-bromo-2-ethoxy-3,4-dihydro-2H-pyran-6-carbonitriles, and about their transformation to 2-ethoxy-2H-pyrans (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 151-164 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloadditions of the α,β-unsaturated-acyl cyanides 1-3 with (Z)-or (E)-1-bromo-2-ethoxyethene (4) may be performed at moderate temperatures and provide in good yields the 3-bromo-2-ethoxy-3,4-dihydro-2H-pyran-6-carbonitriles 5-7, respectively (Scheme 1). Diastereoisomeric pairs of products result at room temperature merely from the ‘endo’- and ‘exo’-transition states; more complex mixtures appear above 60° as a consequence of (Z)/(E)-isomerization of 4. The relative stability of the anomers of 5 and 6 is explored by treatment with BF3·Et2O. Acid alcoholysis (MeOH or EtOH) of 5 leads to acetals 9a, b of 4-bromo-5-oxopentanoate. Alkyl (2Z,4E)-5-ethoxypenta-2,4-dienoates 12, 17, and 20, are formed in alcoholic alkoxide solutions from 5, 6, and 7, respectively, which is compatible with the intermediacy of 2-alkoxy-2H-pyrans and their valence tautomers, α,β-unsaturatedacyl cyanides. Methoxide addition to the CN group competes with dehydrobromination in case of 5; it leads to 3-bromo-3,4-dihydro-2H-pyran-6-carboximidate 13 (ca. 50% at -20°) which can be hydrolyzed to the methyl carboxylate 14. DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) in benzene converts 5 to 6-ethoxy-2-oxohexa-3,5-dienenitrile (11), the ring-opening product of an obviously unstable 2-ethoxy-2H-pyran; the same reagent dehydrobrominates 6 to 2-ethoxy-4-methyl-2H-pyran-6-carbonitrile (15). HBr Elimination from 7 takes place with great ease in presence of pyridine, or even during chromatography on alumina, and leads to the stable ethyl 6-cyano-2-ethoxy-2H-pyran-4-carboxylate (18); this dimerizes at room temperature to give a 1:3 mixture of tricyclic adducts ‘endo’-21 and ‘exo’-21. The structure of the latter is established by an X-ray crystallographic analysis.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780115
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  • 6
    Electronic Resource
    Electronic Resource
    Stereoselectivity of the Radical Reductive Alkylation of Enamines: Importance of the Allylic 1,3-Strain Model (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 2473-2489 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical addition to enamines using Bu3SnH as reducing agent are reported (Schemes 2 and 4). The diastereoselectivity of these reactions was examined in different systems (Tables 1 and 2). Enamines derived from cyclic ketones such as cyclohexanone were alkylated with high diastereoselectivity with preferential formation of the cis-disubstituted cycloalkanes. In acyclic systems such as enamines derived from propiophenone and diethyl ketone, moderate to high stereoselectivities were observed in the H-abstraction step. A model based principally on minimization of allylic 1,3-strain (A1,3 strain) was deduced from the experimental results and semi-empirical (AM1) calculations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760707
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  • 7
    Electronic Resource
    Electronic Resource
    Preparation of 1-Hydroxycyclopentanecarboxylic Acid Derivatives from a Chiral Equivalent of Glycolic Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 477-483 
    Details
    ISSN: 1434-193X
    Keywords: Radical reactions ; Glycolic acid ; Asymmetric synthesis ; Annulation ; Selenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The stereoselective preparation of 1-hydroxycyclopentanecarboxylic acid derivatives is reported. The key reaction is either a radical cyclization or a radical annulation mediated by the transfer of a phenylseleno group. The radical precursors are easily synthesized by two consecutive enolate alkylations. Excellent stereochemical control for the quaternary C(1) stereogenic center has been achieved.
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  • 8
    Electronic Resource
    Electronic Resource
    Atropisomeric Transition State Analogs (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1365-1372 
    Details
    ISSN: 1434-193X
    Keywords: Atropisomerism ; Transition states ; Enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Transition state mimicry is one of the most powerful concepts in enzyme inhibitor design and has led to the development of catalytic antibodies. Transition state analogs are compounds with a fixed shape that resemble the geometry and charge distribution of the transition state of a given reaction. Stabilization of a transition state like conformation is most often achieved by incorporating a ring system into the analog. We show herein that atropisomerism can be used as a new principle for enforcing a transition state like conformation. Atropisomerism relates to the existence of stereoisomers of structurally constrained molecules due to a frozen rotation about a single bond, as for example in binaphthol. The 1-aminomethylnaphthalene derivative 1 exhibits atropisomerism due to a frozen rotation about the C(1)-C(methylene) single bond, which holds the dihedral angle θ[C(2)-C(1)-C(methylene)-N] close to 90°. Compound 1 mimics the transition state for hydride transfer between 1,4-dihydroquinolines 4 and acetone.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    X-ray Structures of a Phenanthroline-Strapped Porphyrin and Its Dihydrated Zinc(II) Complex: Convergent Distal Hydrogen Bonds and “CH···O” Interactions (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1175-1179 
    Details
    ISSN: 1434-1948
    Keywords: Hydrogen bonds ; Inclusion compounds ; Solid-state structures ; Porphyrinoids ; Zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structure of a phenanthroline-(phen-)strapped 1,10-diphenylporphyrin 1 has been resolved. From the structure obtained, it is apparent that in spite of the rigidity of the strap the porphyrin ring is only slightly distorted, and that the substituents on the phen moiety define what would seem to be a hydrophobic pocket. Metallation of the free base 1 with zinc(II) acetate yields a metallic complex (1)Zn with a free axial coordination site. Crystallization of the zinc complex in the presence of a hindered base (N-methylimidazole, denoted N-MeIm) in organic solvents affords single crystals of a porphyrinatozinc(II) species, in which two water molecules are surprisingly present in the encumbered (distal) pocket of the phen site. One water molecule is axially bound to the zinc(II) ion, while the other is doubly hydrogen-bonded, as an H-bond donor to the phenanthroline and as an H-bond acceptor to the axial water ligand.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Face Selectivity of the Diels-Alder Reaction of Hexadienone Moieties Grafted onto the Bicyclo[2.2.2]octene Skeleton and Perturbed by a Remote Tricarbonylbutadieneiron Group (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 1362-1372 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selective oxidations of bis(tricarbonyliron) complexes of methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-2-ylidene)methyl ketones 15-17 afforded selectively the tricarbonyl {(1RS,4SR,7SR,8RS)-C,7,8,C-η-[methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-(2Z)-2-ylidene)methyl ketone]}iron (12), the corresponding (2E)-derivative 13 and the tricarbonyl{(1RS,2RS,3SR,4SR)-C,2,3,C-η-[methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-(2Z)-2-ylidene)methyl ketone]}iron (18). The stereoselectivity of the Diels-Alder reactions of the uncomplexed (Z)- and (E)-hexadienone 12 and 13, respectively, was established. The face of the diene syn with respect to the C(5), C(6) etheno bridge was preferred for the cycloadditions of N-phenyltriazolinedione (NPTAD). In contrast, the reactions of dimethyl acetylenedicarboxylate (DMAD) and methyl propynoate showed a slight preference for addtion to the face of the hexadienones anti with respect to the etheno bridges of 12 and 13. The crystal structure of the adduct 25 resulting from the cycloaddition of NPTAD to 12 is reported.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680529
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