Ammonium chloride catalyzed one-pot synthesis of diindolylmethanes under solvent-free conditions

It has been found that ammonium chloride, which is a very inexpensive and readily available reagent, can efficiently catalyzed electrophilic substitution reactions of indoles. Diindolylmethanes were afforded by reaction of indoles with aldehydes and ketones under solvent-free conditions at 90 °C in the presence of ammonium chloride in good to excellent yields.