Chemoselectivity of Multicomponent Condensations of Barbituric Acids, 5-Aminopyrazoles, and Aldehydes

Multicomponent cyclocondensations between 5-aminopyrazoles, barbituric acids, and aromatic aldehydes under conventional thermal heating, microwave irradiation, or ultrasonic irradiation were studied and the temperature regime was found to be the main factor in controlling their chemoselectivity. At high temperatures the starting materials react in two different ways yielding pyrazolo[4',3':5,6]pyrido[2,3-d]pyrimidines or their dihydro analogues depending on the nature of the N-substituent in the 5-aminopyrazole. Treatment at room temperature results in a new four-component reaction giving previously undisclosed heterocyclic compounds. 4,6-diaryl-1.4,6,7-tetrahydro-2'H-spiro[pyrazolo[3,4-b]pyridine-5,5'-pyrimidine]s. Facile multipurpose three-component selective procedures to new spiroheterocycles are proposed.