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  • Synthetic methods  (3)
  • Wiley-Blackwell  (3)
  • American Chemical Society
  • PANGAEA
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  • Wiley-Blackwell  (3)
  • American Chemical Society
  • PANGAEA
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  • 1
    Electronic Resource
    Electronic Resource
    The Preparation of 2,3,5-Tri- and 2,3-Disubstituted Furans by Regioselective Palladium(0)-Catalyzed Coupling Reactions: Application to the Syntheses of Rosefuran and the F5 Furan Fatty Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2045-2057 
    Details
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Palladium ; Cross-coupling ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5-acceptor-substituted 2,3-dibromofurans 1 and 2 underwent a regioselective Pd0-catalyzed coupling reaction at the C-2 carbon atom. With alkynes the corresponding 2-alkynylfurans 4 and 5 were accessible (49-97% yield). Alkyl-, aryl-, and alkenylzinc reagents gave the 2-substituted furans 8 starting from compound 2 (66-84% yield). The 2-allylfurans 8e and 8f were obtained by a regioselective Stille coupling in 79% and 73% yield. The latter reaction was also applied to the parent 2,3-dibromofuran (27) and yielded the substitution product 28 (60% yield). Subsequent Pd0-catalyzed reactions to introduce a methyl group in 3-position by a methyldebromination were successfully conducted for 2-alkynyl-3-bromofurans with MeZnCl and PdCl2(PPh3)2 as the catalyst in THF (reflux) to yield compounds 13-16 and 24 (67-76%) and with SnMe4 and PdCl2[P(o-Tol)3]2 as the catalyst in DMA (90 °C) for the 2-allyl-3-bromofuran 8e to yield 18 (70%). The more facile reaction of the 2-alkynylfurans relative to those of furans bearing an sp3-carbon atom at C-2 appears to be due to steric reasons. Studies on the 2-alkyl-3-bromofuran 20 supported this notion. With the regioselective coupling methodology the terpene rosefuran (22) was prepared in four steps starting from furan 2 (35% yield overall). The F5 furan fatty acid (26) was synthesized from furan 1 in five steps (29% yield overall).
    Additional Material: 4 Tab.
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  • 2
    Electronic Resource
    Electronic Resource
    The Preparation of N-tert-Butyloxycarbonyl-(Boc-)Protected Sulfoximines and Sulfimines by an Iron(II)-Mediated Nitrene Transfer from BocN3 to Sulfoxides and Sulfides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1033-1039 
    Details
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Iron ; Imidation ; Sulfur ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The imidation of sulfides and sulfoxides to the corresponding sulfimides and sulfoximides was carried out with N-tert-butyloxycarbonyl azide (BocN3) in the presence of FeCl2. Sulfoxides 1 reacted at room temperature in CH2Cl2 to give the corresponding sulfoximides 3 in 40-95% yield. The imidation of the sterically congested substrate tert-butyl methyl sulfoxide (1f) proceeded sluggishly (10% yield). The sterospecificity of the reaction was demonstrated with the enantiomerically enriched substrates (R)-(+)-1b and (S)-(-)-1d which yielded the sulfoximides (R)-(+)-3b and (S)-(-)-3d with retention of configuration. Mechanistically, an intermediate (nitrene)FeIV complex is postulated as the reactive nitrene transfer reagent which is formed from FeCl2 and BocN3. The more nucleophilic sulfides 2 reacted more readily in the imidation than sulfoxides. Their conversion to the corresponding sulfimides 4 was conducted with BocN3 and a substoichiometric amount of FeCl2 (0.25 equiv.). Yields ranged between 44 and 92%. In an alternative reaction mode, BocN3 was utilized at 0°C in the presence of FeCl2 and acetyl acetone. The sulfimidation, which did not otherwise occur at this temperature, was accelerated by the ligand (36-90% yield).
    Additional Material: 4 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    The Paternò-Büchi Reaction of 3-Heteroatom-Substituted Alkenes as A Stereoselective Entry to Polyfunctional Cyclic and Acyclic MoleculesDedicated to Professor G. A. Olah on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1627-1634 
    Details
    ISSN: 0947-3440
    Keywords: Photochemistry ; Synthetic methods ; Oxetanes ; Diols ; Amino alcohols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of 3-heteroatom-substituted oxetanes by the Paternò-Büchi reaction, and their application in synthesis are reviewed. 3-Oxetanols and 3-aminooxetanes are the two most important oxetanes in this respect. By tuning the electronic properties of the enol and enamine substrates, a successful photocycloaddition to carbonyl compounds, with high yield, is possible. Since the oxetane formation proceeds stereoselectively, diastereomerically pure products are readily accessible, which can then be used in further transformations. To this end, regioselective ring-opening reactions have been developed, some of which will be discussed in this account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970803
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