Ultrasound Assisted Domino Strategy for the Synthesis of 2-Aryl-4-(indol-3-yl)-4H-chromenes under Mild Conditions

An efficient and practical approach has been developed for the rapid synthesis of indolyl-chromene derivatives. Ultrasound assisted three component reaction of salicylaldehyde, acetophenone and indole leads to the indolyl 4H-chromene products in good yields. Pyrrolidine base and ethanol medium are employed to achieve desired compounds within short time and at room temperature. We have also shown the catalytic activity and usefulness of the present method by describing the TOF and TON measurement. Beside the present method includes a metal-free process, greener solvent, broad range of substrate scope, and mild conditions.