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  • Organic Chemistry  (5)
  • Carbohydrates  (2)
  • Norartemeseol, rac-  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Product Analysis in the Iodine(III)-Promoted Oxidation of Carbohydrate-Derived Cyclic Enol Ethers: A Mechanistic Study (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2125-2132 
    Details
    ISSN: 0947-3440
    Keywords: Carbohydrates ; Glycals ; Hypervalent iodine ; Mechanism ; Ring-contraction ; Tetrahydrofurans ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study on the mechanism of the well-documented hypervalent iodine-mediated allylic oxidation of glycals leading to 2,3-dihydro-4H-pyran-4-ones is presented. Notable features are the isolation of ring-contracted by-products 6 and 7, which are produced upon oxidation of per-O-benzylated glycal 4, as well as the characterization of carbohydrate-derived tetrahydrofurfurals 12a and 13a, which are formed by the conformation-dependent oxidation of glycals 9a and 10b. In addition, the iodine(III)-mediated oxidation process has been studied by in situ NMR spectroscopy of lyxo-configured glycals 14a,b. Intermediate alkylphenyliodonium species 19b,d and 2-enoyranosides 16a and 20a have been characterized by their NMR signals. These data support a plausible mechanism that is initiated by electrophilic attack of the iodine(III) reagent on the electron-rich enol ether double bond of the glycal. This is followed by the breaking of a bond β,γ-positioned in relation to the carbohydrate-bound iodine and subsequent reductive elimination of iodobenzene. Thus, depending on the glycals employed, a number of diverse oxidation products may be formed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971015
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of Functionalized Cyclopentanes, Cyclohexanes and Cycloheptanes by a Silicon-Induced Domino Reaction (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1811-1821 
    Details
    ISSN: 0947-3440
    Keywords: Domino reaction ; Functionalized cyclopentanes, -hexanes and -heptanes ; Tetrahydrofurans ; Oxetanes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Functionalized cyclopentanes, -hexanes and -heptanes are obtained by addition of lithiated silyldithioacetals 7 to epoxyhomoallyl tosylates 4-6, The reaction involves a cascade of epoxide ring opening, of Brook 1,4-rearrangement and tosylate substitution. The method is particularly suitable for the preparation of cyclopentanes, whereas cyclohexanes and -heptanes are formed in yields only up to 49%. Use of enantiomerically pure epoxides provides optically active cyclopentanes (S)-10b, d, 11a as well as oxetanes (S)-14a, b. Hydrolysis of the dithioacetal function leads to the corresponding ketones 12, Cyclization of epoxide 24b gives an anellated cyclopentane 26, the configuration of which was established by X-ray structural analysis of dinitrobenzoate 27. Use of epoxide 29b provides the anellated tetrahydrofuran 30.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961115
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  • 3
    Electronic Resource
    Electronic Resource
    Hypervalent Iodine and Carbohydrates - A New Liaison (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2267-2274 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycals ; Hypervalent iodine ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthetic applications of hypervalent iodine reagents in the oxidation state +3 in relation to unsaturated carbohydrates are reviewed. By using the Koser reagent or its bis(azido) derivative, fully protected glycals are oxidatively deblocked in the allylic position. The reaction furnishes carbohydrate-derived 2,3-dihydro-4H-pyranones, which serve as starting materials for the preparation of C-saccharides, glycosyl stannanes or thromboxane A2-analogues. Alternatively, iodine(III) reagents can be used to oxidize halide anions. The halogen-ate complexes thus generated behave like synthetic equivalents of acyl hypobromite and iodite, respectively, or halogen azides, which can all add to alkenes, including glycals, under very mild conditions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    (Diacetoxyiodo)benzene DIB - a Multitalented Oxidant in Organic Synthesis (1998)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 184-186 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19983400215
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  • 5
    Electronic Resource
    Electronic Resource
    3,4-bis(O-tert-butyldimethylsilyl)-6-O-tosyl-D-glucal: A probe for the mechanism of the iodine(III)-promoted allylic oxidation of glycals (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 2053-2056 
    Details
    ISSN: 0947-3440
    Keywords: 2,3-Anhydropyranose ; Glycal ; Hypervalent iodine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 3,4-bis(O-tert-butyldimethylsilyl)-6-O-tosyl-D-glucal 4 with the Koser reagent [PhI(OH)OTs] unexpectedly afforded tetrahydrofurfural 6 as well as 2,3-anhydropyranose 7 as major products. This unprecedented, stereoselective transformation helps to gain further insight into the mechanism of the well-documented hypervalent iodine-promoted allylic oxidation of cyclic enol ethers. A novel chemoenzymatic method for the preparation of glucal 4 in high yield is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199511289
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  • 6
    Electronic Resource
    Electronic Resource
    Synthese von rac-Norartemeseol (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 933-936 
    Details
    ISSN: 0170-2041
    Keywords: Norartemeseol, rac- ; Allyl anion, hetero-substituted ; Oxiranes, ring-opening ; Tetrahydrofuran, substituted ; Cyclopropane, vinyl- ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of rac-NorartemeseolThe synthesis of the terpenoid rac-norartemesol (1b) is accomplished using epoxide ring-opening reactions as key steps. Thus, addition of the thio-substituted allyl anion 2b to ethylene oxide followed by proton-induced cyclisation provides the tetrahydrofuran 4a. The oxirane 6, which is formed by simple functional group interconversion, is opened by the diethylaluminium salt 10 of a propargylsilane. After catalytic hydrogenation and tosylation, fluoride-induced cyclisation of the allylsilane 13 gives the target molecule 1b.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1991199101159
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