A green and one-pot synthesis of a library of 1,4-dihydropyrano[2,3-c]-pyrazole-5-carbonitrile derivatives using thiourea dioxide (TUD) as an efficient and reusable organocatalyst

The efficacy of thiourea dioxide (TUD) as an efficient, inexpensive, and readily accessible organocatalyst for the synthesis of 1,4-dihydropyrano[2,3-c]-pyrazole-5-carbonitrile derivatives via a four-component reaction of ethyl acetoacetate, hydrazine hydrate, aryl aldehydes, and malononitrile is described. Upon completion of the reaction, the product was isolated by filtration, and the remaining aqueous TUD solution could be reused several times with consistent catalytic activity. High yields, simple work-up process, avoiding the use of organic solvents, short reaction time, and recyclable catalyst are the superior advantages of the present protocol. [GRAPHICS] .