Practical synthesis and electronic study of non-spiro and spiropyrano[2,3-c]pyrazole-3-carboxylate derivatives via uncatalyzed domino one-pot, four-component reactions

A practical and efficient synthesis of non-spiro and spiropyrano[2,3-c]pyrazole-3-carboxylate derivatives was developed. The synthesis was achieved via a domino one-pot, four-component reaction of diethyl oxaloacetate, hydrazine, aldehyde and malanonitrile in refluxing acidic ethanolic solution under non-catalytic system. This method is rapid, simple and provides products in good yields and can be accessed via different classes of carbonyls, malanonitriles and hydrazine derivatives. Mechanistic study envisaged that this domino four-component reaction proceeds via sequential reactions of pyrazolone formation, Michael reaction and Thorpe-Ziegler cyclization reaction. Strong electronic effects of Knoevenagel and pyrozolone product contribute significantly towards successful cyclization of the title compounds.