Ecofriendly and sustainable efficient synthesis of bis(indolyl)methanes based on recyclable Bronsted (CSA) or Lewis (ZrOCl2•8H2O) acid catalysts

A simple, highly efficient, environmentally benign synthesis of bis(indolyl)methanes and bis(indolyl)glycoconjugate by electrophilic substitution reaction of indole or methylindoles with a variety of aldehydes or simple ketones catalysed by 5 mol% of camphor sulphonic acid (CSA) or zirconium oxychloride octahydrate (ZrOCl(2 center dot)8H(2)O) in aqueous medium (20% EtOH-H(2)0) at ambient temperature is reported. The reactions also proceed efficiently with recovered catalyst (CSA or ZrOCl(2 center dot)8H(2)O) and under scale-up condition.