N-Vinyl-2-(trifluoroacetylethynyl)pyrroles and E-2-(1-bromo-2-trifluoroacetylethenyl)pyrroles: Cross-coupling vs. addition during CH-functionalization of pyrroles with bromotrifluoroacetylacetylene in solid Al2O3 medium. H-bonding control

Add time:09/27/2019    Source:sciencedirect.com

A topochemical reaction of pyrroles with bromotrifluoroacetylacetylene proceeds in solid Al2O3 at room temperature in two different directions depending on the substituent character at the nitrogen atom. While N-vinylpyrroles undergo the cross-coupling to give N-vinyl-2-(trifluoroacetylethynyl)pyrroles in up to 58% yield, unsubstituted NH-pyrroles add to the triple bond to afford exclusively E-2-(1-bromo-2-trifluoroacetylethenyl)pyrroles in 12–21% yields. It has been shown (1H NMR, quantum-chemical calculations) that the reaction is controlled by the strong intramolecular hydrogen bonding between NH and carbonyl groups.

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