title: Synthesis of 5-acetyloxazoles and 1,2-diketones from β-alkoxy-β-ketoenamides and their subsequent transformations.
abstract: Lithiated alkoxyallenes, nitriles, and carboxylic acids have been employed as precursors in a three-component reaction leading to highly substituted β-alkoxy-β-ketoenamides. Upon treatment with trifluoroacetic acid, these enamides could be easily cyclized to 5-acetyloxazole derivatives. The synthesis is very flexible with respect to the substitution pattern at C-2 and C-4 of the oxazole core. A mechanistic suggestion for the oxazole formation is presented on the basis of (18)O-labeled compounds and their mass spectrometric analysis. In several cases, 1,2-diketones are formed as side products or even as major components. The acetyl moiety at C-5 of the oxazole derivatives can efficiently be converted into alkenyl or alkynyl moieties, which allows a multitude of subsequent reactions. Condensation reactions of the acetyl group provided the expected oxime or hydrazone. By applying a Fischer reaction, the phenylhydrazone could be transferred into an indole, which emphasizes the potential of 5-acetyloxazoles for the preparation of highly substituted (poly)heterocyclic systems. The alkynyl group at C-2 is prone to addition reactions, providing an enamine with interesting photophysical properties. Sonogashira couplings were performed with 5-alkynyl-substituted oxazoles, furnishing the expected aryl-substituted products. This alkynyl unit was employed for the preparation of a new, star-shaped trisoxazole derivative. The ability of this multivalent compound to form self-assembled monolayers between the basal plane of highly oriented pyrolytic graphite and 1-phenyloctane was demonstrated by scanning tunneling microscopy (STM). The star-shaped compound seems to prefer the C(3)-symmetric arrangement in this two-dimensional crystal. Two 1,2-diketones were smoothly converted into functionalized quinoxaline derivatives.
authors: Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany.
authors: Tilman
authors: T
authors: Lechel
authors: Markus
authors: M
authors: Gerhard
authors: Daniel
authors: D
authors: Trawny
authors: Boris
authors: B
authors: Brusilowskij
authors: Luise
authors: L
authors: Schefzig
authors: Reinhold
authors: R
authors: Zimmer
authors: Jürgen P
authors: JP
authors: Rabe
authors: Dieter
authors: D
authors: Lentz
authors: Christoph A
authors: CA
authors: Schalley
authors: Hans-Ulrich
authors: HU
authors: Reissig