Microwave-Assisted, Solvent-Free Bischler Indole Synthesis

The solid-state reaction between anilines and phenacyl bromides in the presence of an equimolecular amount of sodium bicarbonate gives N-phenacylanilines. Microwave irradiation of mixtures of these compounds with anilinium bromides at 540 W for 45-60 s provides a mild, general, and environmentally friendly method for the synthesis of 2-arylindoles in 50-56% overall yields. A one-pot variation of the method, involving irradiation of 2:1 mixtures of anilines and phenacyl bromides, was also developed, allowing a simplified experimental procedure and leading to improved yields (52-75%).