Regioselective Friedel–Crafts Acylation of Indoles Catalysed by Zinc Oxide in an Ionic Liquid

Abstract

A facile method for the regioselective Friedel-Crafts acylation of indoles with acyl chlorides catalysed by zinc oxide in an ionic liquid medium has been developed. The corresponding 3-acylindoles were obtained in good to high yields under mild reaction conditions. Zinc oxide, which is easily available and requires no special handling procedures, is an efficient catalyst for acylation of indoles.

A Simple, Effective, Green Method for the Regioselective 3-Acylation of Unprotected Indoles

“…Regioselectivity in the 3-acylation of indoles has been an interesting and challenging subject in organic synthesis. A wide range of 3-acylindoles was synthesized by several methods such as Friedel-Crafts acylation [5][6][7][8][9][10][11][12], Vilsmeier-Haack type reaction [4,13], α-aminocarbonyl compounds with palladium [14], carbamoyl electrophiles [2], α-oxocarboxylic acids [15][16][17], and nitrilium salt with palladium [18]. Among those, Friedel-Crafts acylation of free (NH) indoles is definitely the simplest way [19], however, low yields were observed due to competing substitution at the 1-position.…”