Introduction to the novel ionic liquid-based catalytic system for the multicomponent preparation of benzo[f]pyrano[3,2-c]chromene and pyrano[3,2-c]chromene derivatives under ultrasonic irradiation condition

Abstract

A straightforward and high-productivity procedure for preparing benzo[f]pyrano[3,2-c]chromene derivatives is reported. 7 compounds coded as 1a-7a were prepared by a three-component reaction between 1-hydroxy-3H-benzo[f]chromen-3-one, malononitrile, and 1-benzylindoline-2,3-dione in ethanol under reflux condition and ultrasonic irradiation. Similarly, 10 compounds (1b-10b) of pyrano[3,2-c]chromene derivatives were prepared from the three-component reaction between 4-hydroxycoumarin, malononitrile, and aromatic aldehydes. Ionic liquid B₂ was prepared for the first time and used as a catalyst. The nonchromatographic separation and purification of the products with high-yield productivity are the salient features of this protocol.