Takudrei

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Synthesis of 5-Acetyloxazoles and 1,2-Diketones from ß-Alkoxy-ß-ketoenamides and their Subsequent Transformations

T. Lechel, M. Gerhard, D. Trawny, B. Brusilowskij, L. Schefzig, R. Zimmer, J. P. Rabe, D. Lentz, C. A. Schalley, H.-U. Reißig— 2011

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 18O-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 C3-symmetric arrangement in this two-dimensional crystal. Two 1,2-diketones were smoothly converted into functionalized quinoxaline derivatives.

Title155
Synthesis of 5-Acetyloxazoles and 1,2-Diketones from ß-Alkoxy-ß-ketoenamides and their Subsequent Transformations
AuthorT. Lechel, M. Gerhard, D. Trawny, B. Brusilowskij, L. Schefzig, R. Zimmer, J. P. Rabe, D. Lentz, C. A. Schalley, H.-U. Reißig
Date20110528
IdentifierDOI 10.1002/chem.201100382
Source(s)
CitationChem. Eur. J. 2011, 17, 7480-7491