Brønsted acid ionic liquid catalyzed facile synthesis of 3-vinylindoles through direct C3 alkenylation of indoles with simple ketones

A direct dehydrative coupling protocol for the synthesis of 3-vinylindoles using easily available indoles and simple ketones as substrates was developed with the aid of a sulfonyl-containing Brønsted acid ionic liquid. The salient features of this protocol are high synthetic efficiency, a metal- and solvent-free system, a recyclable catalyst, mild conditions and easy product isolation. With the ionic liquid catalyst, a hitherto unreported straightforward method for the construction of the indolo[3,2-b]carbazole skeleton was also developed using 2-hydroxymethylindole and acetophenone as starting materials.