[4+2] Annulation of 3-(2,2-diethoxyethyl)-1,3-dicarbonyl compounds with indoles catalyzed by Brønsted acid ionic liquid for the synthesis of carbazoles.

Graphical abstract Highlights • Various carbazoles were synthesized via [4+2] annulation. • 1,3-Dicarbonyl compounds and indoles afforded excellent yields of carbazoles. • A Brønsted acid ionic liquid was proven to be effective catalyst for this reaction. • The ionic liquid catalyst can be recycled at least three times. Abstract Various carbazoles were synthesized via [4+2] annulation of 3-(2,2-diethoxyethyl)-1,3-dicarbonyl compounds with indoles. A Brønsted acid ionic liquid, [BPy]HSO 4 , was proven to be effective catalyst for this reaction. The ionic liquid catalyst can be recycled three times without significant loss of its catalytic activity. [ABSTRACT FROM AUTHOR]