Amberlyst 15 efficiently catalyzed the electrophilic substitution reaction of indoles with isatin derivatives to afford 3,3-di(indolyl)oxindoles in water. An important feature of this protocol is the reaction of 3-methyl-1H-indole with isatins to give the corresponding 3,3-diaryloxindole derivatives in high yields. The catalyst exhibited remarkable reusable activity.
