Thiourea dioxide in water as a recyclable catalyst for the synthesis of structurally diverse dihydropyrido[2,3-d]pyrimidine-2,4-diones

A series of dihydropyrido[2,3-d]pyrimidine-2,4-diones derivatives were synthesized by the three-component reaction of 6-amino-1,3-dimethyl uracil, aromatic aldehydes, and 1,3-dicarbonyl compound catalyzed by thiourea dioxide in aqueous media. Importantly, the aqueous layer containing thiourea dioxide could be reused for several runs without significant loss in catalytic activity. This method provided several advantages such as inexpensive, recyclable catalyst, easier work-up, milder reaction conditions and environmental benign nature.