A highly promising approach for the one-pot synthesis of biscoumarins using HY zeolite as recyclable and green catalyst

Abstract

Biscoumarins, the bridge substituted dimers of 4-hydroxycoumarin, are distinguished derivatives of coumarin. In view of numerous pharmaceutical applications of biscoumarins, the construction of appropriate one-pot synthetic methods for their preparation has been a subject of great attention in recent years. In continuation of ongoing study for the construction of promising approaches for the preparation of biscoumarins, herein we report a zeolite-mediated methodology, in which zeolites, for example, NaY, HY, HZSM-5 and H-beta were employed as catalysts to investigate their catalytic potencies in the synthesis of biscoumarins. In this approach, aromatic aldehydes were treated with 4-hydroxycoumarin in the presence of zeolite catalyst in refluxing ethanol for 2–3 h to furnish biscoumarins in 80–96% yield. The yield of biscoumarins increased in the following order NaY < HZSM-5 < H-beta < HY. Aldehydes both with electron-donating and electron-withdrawing units underwent smooth conversion to their respective biscoumarins without the development of any side products. The cost-effective, eco-friendly and ready available zeolite catalyst could be recovered and reused several times. This methodology offers operational simplicity and avoids the use of toxic solvents and corrosive reagents. The present approach offers remarkable advantages such as high catalytic activity, straight-forward procedure, simple workup and low catalyst loading.