Organo-Catalytic Approach for Biscoumarin Synthesis via a Biomass-Derived Sustainable Strategy

Biscouamrins are dimers of 4-hydroxycoumarin formed by reaction of aldehydes and 4-hydroxycoumarin. These were synthesized via one-pot pseudo three component cascade reaction using sugar ionic liquid as an organo catalyst under green reaction conditions. Sugar derived from natural carbohydrates were used in the formulation of D-ribose sugar ionic liquid (RSIL). In the formation of biscouamrins two reactions occurs i. e., Knoevenagel condensation and Michael addition reaction. Substituted aliphatic, aromatic and heterocyclic aldehydes were used for the synthesis of a variety of target biscouamrins products and developed protocol is scalable. Substitutions in the aryl ring of benzaldehyde showed very less or no effect on the reaction rate. The developed catalyst was shown to be recyclable five times without losing much of its efficiency.