A sustainable one-pot multicomponent synthesis of dihydropyrano[3,2-c]chromenes and
2-aminochromenes was developed using [AcMIm]Cl, a task-specific acidic ionic liquid
catalyst, under mild, solvent-free conditions. The present protocol affords dihydropyrano[3,2-c]chromenes in excellent yields (93–99%) with a short reaction time (4–5 min), and
comparable efficiency was observed for the 2-aminochromenes (90–92%). The bifunctional
[AcMIm]Cl bears an acidic carboxyl (–COOH) and a basic imidazolium nitrogen, which
act synergistically to activate both the aldehyde carbonyl and the malononitrile C–H
bond, thereby accelerating the reaction. The major advantages of this method include
a simple workup: no volatile organic solvent, and the solid products were purified
by recrystallization from hot ethanol without chromatography. These features render
the present method environmentally benign and economically advantageous than conventional
approaches.
Keywords
Task-specific ionic liquid - [AcMIm]Cl - Dihydropyrano[3,2-
c]chromenes - 2-Aminochromenes - One-pot multicomponent reactions - Green synthesis
