Trifluoroacetylation of indole-chalcones derived from the 2-amino-3-(arylethynyl)-5-bromo-iodochalcones

• Alkynylation of the 2-amino-5-bromo-3-iodochalcones affords the 8-alkynylated derivatives.
• Palladium chloride-mediated endo-dig cyclization affords indole-chalcone derivatives.
• Trifluoroacetylation of the indole-chalcones occurs at the C-3 position of the indole ring.
• Single-crystal X-ray diffraction confirms the E-geometry of the indole-chalcones.

The present work describes a novel approach for the annulation of an indole moiety onto the 1,3-diaryl-2-propen-1-one scaffold followed by trifluoroacetylation of the resultant indole-based chalcones to afford the corresponding 3-trifluoroacetylindole-chalcone derivatives. The parent indole-chalcones were themselves prepared via palladium catalysed Sonogashira cross-coupling of the corresponding 2-amino-5-bromo-3-iodochalcone precursors with arylacetylenes followed by palladium chloride-mediated endo-dig cyclization of the incipient 3-arylalkynyl-substituted 2-aminochalcones. The structures of all the prepared compounds were characterized using a combination of NMR (1H, 13C, 19F) and IR spectroscopic techniques as well as mass spectrometry. The geometry of the indole-chalcones and their 3-trifluoroacetyl substituted derivatives were established by means of 1H NMR spectroscopy complemented by single crystal X-ray crystallography. Single crystal X-ray structure of compound 5a revealed the existence of an inversion twin in the asymmetric unit.

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