Greener construction of 4H-chromenes based dyes in deep eutectic solvent

Abstract

Green solvents such as deep eutectic solvents are new emerging alternatives to the conventional harmful organic solvents which may find a number of interesting applications in industrial and chemical processes. A facile, atom-economic and environmentally-benign one-pot reaction of salicylaldehyde and malononitrile with various nucleophiles, including indoles, thiols, secondary amines, cyanide and azide were efficiently achieved in choline chloride based deep eutectic solvent (DES). Products distribution of the current green protocol depend on the nature of the nucleophile used in the reaction. The one-pot reaction of salicylaldehyde derivatives and malononitrile with thiols, indoles, and cyanide give 2-amino-3-cyano-4H-chromene derivatives. Secondary amines result in the formation of benzopyrano[2,3-d] pyrimidines, due to the further reaction of salicylaldehyde with 4H-chromene under the same reaction condition. The DES was recycled without any reduction in activity or yield. Therefore, the synthesis of chromene based dyes in green solvents at room temperature under catalyst-free conditions is a promising alternative to previously used procedures.