highly efficient synthesis of dicoumarols and xanthene derivatives in presence of brønsted–lewis acidic ionic liquids catalyst

A series of metal chloride-based acidic ionic liquids have been prepared and used as an efficient catalyst in one-pot multicomponent synthesis of biscoumarins and substituted xanthenes derivatives under solvent-free conditions. among the acidic ionic liquids, n-methylpyrrolidonium zinc chloride (hnmp/zncl3)-based brønsted–lewis acidic ionic liquids were found to be an effective and recyclable catalyst for a one-pot synthesis of biscoumarins through the domino knoevenagel–michael reaction of a variety of aldehydes with 4-hydroxycoumarin in short reaction times. the reactions which occur under relatively mild conditions afforded the biscoumarin derivatives employing a very low loading of catalyst in satisfactory isolated yields and high purity after simple work-up. the brønsted–lewis acidic ionic liquid catalyst was reused four times without any variation in yield.