Glycine Catalyzed One-Pot Three-Component Synthesis of Structurally Diverse 2-Amino Substituted Pyran Annulated Heterocycles in Aqueous Ethanol under Refluxed Conditions

Introduction: A facile, convenient and general method has been developed for the one-pot three-component synthesis of structurally diverse 2-amino pyran annulated heterocycles from the reactions of aromatic aldehydes, malononitrile and various C-H activated acids in the presence of a catalytic amount of glycine as an efficient metal-free organocatalyst in aqueous ethanol under refluxed conditions. Methods: Using this developed protocol, we were able to synthesize a series of structurally diverse 2- amino pyran derivatives viz., 2-amino-4,5-dihydropyrano[3,2-c]chromenes, 2-amino-4,5-dihydropyrano [4,3-b]pyrans, 2-amino-5,6,7,8-tetrahydro-4H-chromenes, 2'-amino-2,5'-dioxo-5'H-spiro[indoline-3,4'-pyrano [3,2-c]chromene]-3'-carbonitrile and 2'-amino-1,3,5'-trioxo-1,3-dihydro-5'H-spiro[indene-2,4'-pyrano[3,2- c]chromene]-3'-carbonitrile in excellent yields. Result: Synthesis of biologically promising pyrans and spiropyrans, high atom economy, excellent yields, use of metal-free catalyst, less toxic solvents, no chromatographic column purifications, multiple carbon-carbon and carbon-heteroatom bond formations are some of the major advantages of this newly developed protocol. Conclusion: In conclusion, we have developed a simple, convenient, and efficient method for the synthesis of a series of structurally diverse 2-amino pyran annulated heterocyclic derivatives.