Zeolite catalyzed electrophilic substitution reaction of indoles with aldehydes: synthesis of bis(indolyl)methanes

Abstract

Zeolites were found to catalyze electrophilic substitution reaction of indole with a variety of aromatic aldehydes affording good to excellent yields of bis(indolyl)methanes at room temperature. Zeolites such as Hβ, HY and H-ZSM-5 were used as catalysts to assess their catalytic activities in the syntheses of bis(indolyl)methanes. Zn 2+ ion-exchanged Y zeolite showed better activity than parent zeolite owing to its higher Lewis acidity. The yield of bis(indolyl)methanes increased in the following order H-ZSM-5<Hβ<HY<ZnY. Presumably the reaction occurs at the outer zeolite surface. The catalyst is readily recyclable and reusable by a simple separation method.