G. Babu et al., A convenient method of synthesis of bis-indolylmethanes: Indium trichloride catalyzed reactions of indole with aldehydes and Schiff's bases., SYN COMMUN, 30(9), 2000, pp. 1609-1614
Anhydrous indium trichloride (InCl3) is found to catalyze the electrophilic
substitution reaction of indole with aromatic aldehydes and Schiffs bases
which resulted in an efficient synthesis of bis-indolylmethanes in good to
excellent yield.