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  • General Chemistry  (77)
  • Structure  (6)
  • 1995-1999  (77)
  • 1935-1939  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of Hetaryl Glycosides and Their Glycosyl Donor Properties (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1353-1360 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Substitution ; Carbohydrates ; Anomeric O-hetarylation ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Anomeric O-hetarylation of tetra-O-benzyl- and tetra-O-acetylglucose (1a, b) can be directly performed with electron-deficient heteroaromatic/heterocyclic systems 2-14, which contain imide halide moieties. The reactions were carried out in the presence of a base and led, through an exchange of the halide by the glucopyranosyloxy moiety, to the products 2a-14a, 7b-14b. Predominantly or exclusively β-products were obtained. Systems bearing more than one imide halide moiety, such as cyanuric fluoride (15) or 5-chloro-2,4,6-trifluoropyrimidine (16), can be employed for successive anomeric O-hetarylations. Investigation of the glycosyl donor properties of O-glucosyl heteroaromatic imidates with 6-O- and 4-O-unprotected glucose derivatives 18 and 19 as acceptors and comparison of the results obtained with data for the corresponding β-trichloroacetimidates 17aβ and 17bβ, reveals that 2,3,5,6-tetrafluoropyridin-4-yl glucopyranosides 14aβ and 14bβ exhibit similar properties. For specific tasks, for instance α-glucopyranoside formation, 14aβ may even be advantageous.
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  • 2
    Electronic Resource
    Electronic Resource
    Kristall- und Molekülstruktur von Arsen-tris(trifluoracetat) (1996)
    Springer
    Monatshefte für Chemie 127 (1996), S. 1215-1220 
    Details
    ISSN: 1434-4475
    Keywords: Coordination of As(III) ; Structure ; Stereoisomeres
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary Arsenictris(trifluoroacetate) (1) crystallizes monoclinic in the space group Cc witha=1229.3,b=1697.9,c=1243.5 pm, β=110.01°, andZ=8. The trifluoroacetic acid ions acts as chelating ligands. Additionally they are bridging crystallographic independent molecules. As has a coordination number of 3+3(+2). The unit cell contains two sets of chirameres.
    Notes: Zusammenfassung Arsen-tris(trifluoracetat) (1) kristallisiert monoklin in der Raumgruppe Cc mita=1229.3,b=1697.9,c=1243.5 pm, β=110.01° undZ=8. Die Trifluoracetatanionen fungieren gegenüber As als zweizähnige Liganden und verknüpfen die beiden kristallographisch unabhängigen Moleküle zusätzlich intermolekular. As erreicht dadurch gegenüber O die Koordinationszahl 3+3(+2). Die Elementarzelle enthält zwei Sätze von chirameren Molekülen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807787
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  • 3
    Electronic Resource
    Electronic Resource
    Antimontribenzoat (1995)
    Springer
    Monatshefte für Chemie 126 (1995), S. 1045-1050 
    Details
    ISSN: 1434-4475
    Keywords: Coordination of Sb(III) ; Structure ; Enantiomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary The Δ isomer of (C6H5CO2)3Sb crystallizes rhombohedrally (hexagonal axes) in the space group R3 witha=1944.0 pm,c=422.3 pm, andZ=3. The molecules are stacked parallel to 001; Sb has a coordination number of 3+3 (Sb-O: 208 and 256 pm, resp.).
    Notes: Zusammenfassung Das Δ-Isomer des Antimontribenzoats kristallisiert rhomboedrisch (hexagonale Aufstellung) in der Raumgruppe R3 mita=1944.0 pm,c=422.3 pm undZ=3. Die Moleküle sind parallel zu 001 gestapelt. Sb hat gegenüber O die Koordinationszahl 3+3 (Sb-O: 208 bzw. 256 pm).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811375
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  • 4
    Electronic Resource
    Electronic Resource
    Zur Struktur zweier Arsen- und Antimontricarboxylate (1996)
    Springer
    Monatshefte für Chemie 127 (1996), S. 461-468 
    Details
    ISSN: 1434-4475
    Keywords: Coordination of As(III) and Sb(III) ; Structure ; Enantiomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary Arsen-tris(2,2-dimethylpropionate) (1) crystallizes monoclinic in the space group P21/n witha=926.2,b=2158.6,c=983.7 pm, β=94.92°, andZ=4. As has a coordination number of 3+3. Antimony tripropionate (2) crystallizes monoclinic in the space group P21/c witha=930.2,b=863.0,c=1575.2 pm, β=90.27, andZ=4. The molecules are bridged to chains; therefore, Sb reaches the coordination number 3+3 (+3).
    Notes: Zusammenfassung Arsen-tris(2,2-dimethylpropionat) (1) kristallisiert monoklin in der Raumgruppe P21/n mita=926.2,b=2158.6,c=983.7 pm, β=94.92° undZ=4. As hat gegenüber O die Koordinationszahl 3+3. Antimontripropionat (2) kristallisiert monoklin in der Raumgruppe P21/c mita=930.2,b=863.0,c=1575.2 pm, β=90.27 undZ=4. Die Moleküle sind intermolekular zu Ketten verknüpft, wodurch Sb die Koordinationszahl 3+3 (+3) erreicht.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807070
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  • 5
    Electronic Resource
    Electronic Resource
    Syntheses and Properties of S2-Bridged Benzidines (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2409-2416 
    Details
    ISSN: 1434-193X
    Keywords: Sulfur heterocycles ; Rearrangements ; Reductions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of 1,2-benzodithiino[5,4,3-cde][1,2]benzodithiin-2,7-diamine (1) and dithio-bridged benzidine 2 have been achieved. The starting material for the synthesis of 1 was 1,3-diiodo-5-nitrobenzene (15) which was transformed by conventional means into 1,2-bis[3,5-bis(ethylthio)phenyl]diazane (19). The benzidine rearrangement of 19 in the presence of HBF4 at -30 °C yielded 4,4′-diamino-2,2′,6,6′-tetraethylthiobiphenyl (20) in 50 % yield. Treatment of 20 with sodium in ammonia and work-up in the presence of air yielded 1. The latter compound could be reduced with LiAlH4 to the tetrathiol 20a. The starting material for the preparation of 2 was 3-chloro-1-iodo-5-nitrobenzene (23), a side product of the preparation of 15. It was transformed analogously to the preparation of 1 into 1,2-bis(3-ethylthiophenyl)diazane (28). The benzidine rearrangement of 28 in presence of HBF4 at -30 °C afforded 4,4′-diamino-2,2′-bis(ethylthio)biphenyl (29) in 49 % yield. Treatment of 29 with sodium in ammonia and work-up under aerobic conditions yielded 2. Quantitative reduction of 2 to the thiol 29a could be achieved with LiAlH4. The reversible electrochemical reduction of 1 on unmodified glassy carbon electrodes leads to a product to which the structure of 3 was assigned.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Polar and Steric Substituent Effects in 5-exo-trig Cyclizations of 1-Aryl-4-penten-1-oxyl Radicals (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 523-523 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -By mistake wrong concentrations were given in the footnote of Table 1 and in the Discussion. Instead of c0 = 1.2 M read c0 = 0.12 M if 2-naphthalenethiol was used as hydrogen donor and instead of c0 = 1.8 M read c0 = 0.18 M if Bu3SnH was used to trap photoproducts. In Table 2 relative rate constants of radical 2d refer to radical 2e and vice versa as correctly stated in the Discussion. In the Experimental Section (Iodocyclization) read 2.25 g (8.86 mmol) of iodine instead of 2.25 g (1.10 mmol) of iodine.
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  • 7
    Electronic Resource
    Electronic Resource
    A Novel and Efficient Route towards α-GalNAc-Ser and α-GalNAc-Thr Building Blocks for Glycopeptide Synthesis (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1167-1171 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycals, nitro ; Michael additions ; Glycosylations ; Glycosides, galactosamine ; Reduction, nitro group ; Glycopeptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Michael addition of serine and threonine derivatives 4a-4c to 3,4,6-tri-O-benzyl-2-nitro-D-galactal (1) afforded the corresponding 2-deoxy-2-nitro-α-D-galactopyranosides 5a-5c in good yield and stereoselectivity. 2-deoxy-2-nitroglycosides 5a and 5b were reduced to the 2-acetamido compounds by platinized Raney nickel T4. Manipulation of the protecting groups afforded known N-Fmoc-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-galactopyranosyl)-L-serine (8a) and -threonine (8b), valuable building blocks for O-glycopeptide synthesis.
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  • 8
    Electronic Resource
    Electronic Resource
    C-Disaccharides of Ketoses (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 502-510 
    Details
    ISSN: 0947-6539
    Keywords: alkynes ; C-glycosides ; cobalt complexes ; cyclizations ; enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of gluconolactone 2 with allylmagnesium bromide at low temperatures afforded ketopyranose 3, which could easily be converted into open-chain ketoses (R)-6 and (S)-6. Their reaction with lithioacetylide 9 afforded propargylic alcohol derivatives (R)-10 and (S)-10, which could not be cyclized directly to the desired C-ketosides. They were converted by standard procedures into (R)-14 and (S)-14 and then into dicobalthexacarbonyl complexes (R)-16 and (S)-16. A facile acid-catalyzed ring closure gave the desired C-ketosides (R)-18 α/β and (S)-18α/β, respectively, in different ratios. In order to demonstrate that removal of the protective groups and hydrogenation of the CC triple bond proceed smoothly, (R)-18 α was transformed into the deprotected target molecule (R)-1 α. For the assignment of the new chiral centers at C-2/2′ and at C-8, (S)-18α was transformed into azido derivative (S)-22α, which underwent intramolecular cycloaddition to afford the spiro derivative (S)-25α. Because of the conformational constraints in this molecule, unequivocal configurational assignment was possible with the help of NMR data.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020508
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  • 9
    Electronic Resource
    Electronic Resource
    Photoreactions of phenyl-substituted N-(pent-4-enyl-1-oxy)pyridine-2(1 H)-thiones (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1014-1023 
    Details
    ISSN: 0947-6539
    Keywords: alkoxy radicals ; cyclizations ; pyridinethiones ; radicals ; tetrahydrofurans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of hitherto unknown N-(pent-4-enyl-1-oxy)pyridine-2(1 H)-thiones (6) were prepared from substituted pent-4-enyl tosylates or benzylic chlorides. On irradiation with incandescent light heterocycles 6 liberated alkoxy radicals 2, which were studied for rearrangement reactions. Surprisingly, all transformations involving the 1-phenylpent-4-enyl-1-oxy radical (2a), for example, to give the substituted thioether 8, 2-bro-momethyl-5-phenyltetrahydrofuran (11), or the tetrahydrofuran 14a, were not stereoselective. On the other hand 2-, 3- mono-, and 1,5-disubstituted pent-4-enyl-1-oxy radicals 2d-e and 2g cyclized in good yields and with good to excellent stereoselectivities to give the corresponding 2,4-cis- and 2,3-trans-phenyltetra-hydrofurfuryl radicals 3d-e, and the trans-2-benzyl-5-methyl substituted intermediate 3g. The major reaction mode of the 4-phenylpent-4-enyl-1-oxy radical (2f) was the 6-endo cyclization, which afforded 3-phenyltetrahydropyran (13f) as the major product (endo:exo = 93:7) after trapping with hydrogen donors. According to the experimental data of the present study, the unusual reactivity of the 1-phenylpent-4-enyl-1-oxy radical (2a) in 5-exo-trig ring closures could be caused by a coplanar arrangement of the benzyloxy moiety in the transition state of the cyclization. This interaction would lock the radical center in 2a in a preferred conformation, which would result in similar steric effects for both cis- and trans- cyclizations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020816
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  • 10
    Electronic Resource
    Electronic Resource
    Asymmetric Control in the Pictet-Spengler Reaction by Means of N-Protected Amino Acids as Chiral Auxiliary Groups (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1566-1571 
    Details
    ISSN: 0947-6539
    Keywords: amino acids ; asymmetric syntheses ; carbolines ; chiral auxiliaries ; Pictet-Spengler reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aromatic and aliphatic Schiff bases of tryptamine react with Fmoc- or phthaloyl-protected amino acid chlorides to form N-acyliminium intermediates, which, in the presence of titanium alkoxides at room temperature, undergo Pictet-Spengler reactions to give tetrahydro-β-carbolines with diastereomeric ratios of up to 99:1. The chiral auxiliary can be removed from the Pictet-Spengler adducts by means of a simple reduction. To rationalize the observed stereoselectivity a transition-state model is proposed in which the titanium atom coordinates both the carbonyl group of the N-acyliminium ion and the amino acid protecting group.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021215
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