Ultrasound-Assisted Expedient and Green Synthesis of a New Series of Diversely Functionalized 7-Aryl/heteroarylchromeno[4,3-d]pyrido[1,2-a]pyrimidin-6(7H)-ones via One-Pot Multicomponent Reaction under Sulfamic Acid Catalysis at Ambient Conditions

An ultrasound-assisted, highly efficient, simple, and straightforward protocol for one-pot synthesis of a new series of pharmaceutically relevant and diversely functionalized 7-aryl/heteroarylchromeno[4,3-d]pyrido[1,2-a]pyrimidin-6(7H)-ones (4) was developed based on a three-component tandem reaction between 4-hydroxycoumarin (1), substituted aromatic aldehydes (2), and 2-aminopyridines (3) in the presence of sulfamic acid as a low-cost and ecofriendly solid acid-catalyst in aqueous ethanol at ambient conditions. Expedient metal-free synthesis, good to excellent yields, energy efficiency, use of aqueous ethanol as reaction medium, easy isolation of products, no need of column chromatographic purification, high atom-economy and low E-factor, high turnover number, ecofriendliness, and operational simplicity are some of the salient features of this newly developed protocol.