An efficient and practical synthesis of bis(indolyl)methanes catalyzed by aminosulfonic acid under ultrasound

Synthesis of bis(indolyl)methanes via electrophilic substitution reactions of indoles with aromatic aldehydes and ketones catalyzed by aminosulfonic acid was carried out in 23–96% yield at 30–38 °C in EtOH aqueous solution under ultrasound irradiation.