melamine trisulfonic acid: an efficient and recyclable solid acid catalyst for the green synthesis of biscoumarin derivatives

a novel catalytic synthesis of 3,3'-(arylmethylene)-bis-(4-hydroxy-2h-chromene-2-one) derivatives from a tandem condensation reaction of 4-hydroxycoumarin and aromatic aldehydes has been developed. the reaction occurs in water in the presence of melamine trisulfonic acid as catalyst to give the corresponding products in good to high yields. this green approach has several advantages such as short reaction times, clean reaction profiles, and simple experimental and workup procedures. moreover, the catalyst can be easily recovered by filtration and used at least seven times with only slight reduction in its catalytic activity. the results of the presented protocol in comparison with the different available catalysts in condensation reaction of benzaldehyde with 4-hydroxycoumarin show that mtsa presented better results due to the structure of mtsa.