Facile and One-Pot Access to Diverse and Densely Functionalized 2-Amino-3-cyano-4H-pyrans and Pyran-Annulated Heterocyclic Scaffolds via an Eco-Friendly Multicomponent Reaction at Room Temperature Using Urea as a Novel Organo-Catalyst

A simple, straightforward, and highly efficient multicomponent one-pot synthesis of a pharmaceutically interesting diverse kind of functionalized 2-amino-3-cyano-4H-pyrans and pyran-annulated heterocycles has been developed based on a low-cost and environmentally benign commercially available urea as a novel organo-catalyst. The reaction occurs via tandem Knoevenagel-cyclocondensation of aldehydes, malononitrile, and C H-activated acidic compounds in aqueous ethanol at room temperature. Following this protocol, it was possible to synthesize 2-amino-3-cyano-pyrano[3,2-dchromen5(4H)-ones (4aa-4a1), 2-amino-3-cyano-pyrano[4,3-Idpyran5(4H)-ones (4ba-4be), 2-amino-3-cyano-7,8-dihydro-4H-chromen-5(6H)-one (4ca-4cr), 1H-pyrano[2,3-d]pyrimidine-2, 4(3H,5H)-diones (4da-4dd), 2-amino-3-cyano-5,10-dioxo-5,10-dihydro-4H-benzo[g]chromenes (4ea-4ec), 2-amino-3-cyano-4Hpyrans (4fa-4th), and 1,4-dihydropyrano[2,3-c]pyrazoles (4ga-4gb). The salient features.of the present protocol are mild reaction conditions, excellent yields, high atom-economy, eco-friendly standards, easy isolation of products, no column chromatographic separation, and reusability of reaction media. Bis-pyranization has also been observed in the reactions of terephthaldehyde.