期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 17, 期 42, 页码 11838-11843出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201101739
关键词
allenes; fluorescence; nonaflates; palladium; pyridines; thiophenes
资金
- Alexander von Humboldt Foundation
- Deutsche Forschungsgemeinschaft
- Center for Supramolecular Interactions of the Freie Universitat Berlin
- Bayer Schering Pharma AG
Herein, we describe our attempts to systematically prepare a series of oligo(2-thienyl)-substituted pyridine derivatives. The crucial starting material, a beta-alkoxy-beta-ketoenamide, is easily available on a large scale by the reaction of lithiated methoxyallene with thiophene-2-carbonitrile and thiophene-2-carboxylic acid. This three-component reaction is followed by intramolecular cyclization to yield the suitably functionalized 2,6-di(2-thienyl)-substituted pyridine derivates. The two oxygen atoms allow the programmed activation of positions C-3, C-4, or C-5 of the pyridine ring to perform palladium-catalyzed coupling reactions with thiophene-2-boronic acid or 2-(tributylstannyl) thiophene, and alternatively, reductive removal of groups. With this concept, we were able to prepare five pyridine derivatives with 2-thienyl substituents in the 2,6-, 2,3,6-, 2,4,6-, 2,3,4,6-, and 2,3,5,6-positions. 2,3,4,5,6-Penta(2-thienyl) pyridine was not available with our methods. The UV/Vis and fluorescence spectra of all pyridines were recorded and showed a dependence on the substitution pattern and protonation state. For the protonated 2,3,5,6-tetra(2thienyl)-substituted pyridine, a Stokes shift of about 180 nm with an emission at 515 nm was observed.
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