An NMR and computational study of azolo[a]pyrimidines with special emphasis on pyrazolo[1,5-a]pyrimidines

The reaction of 3(5)-amino-5(3)-hydrazinopyrazole, a bifunctional compound, with 3-oxo-3-phenylpropanenitrile and two of its p-substituted derivatives affords 2,5-diaryl-7-aminopyrazolo[1,5-a]pyrimidines. A mechanism for this unexpected reaction involving the formation of hydrazine is proposed. The position of the aryl substituents on the bicyclic ring has been established by the combined use of NMR and DFT calculations. Moreover, the chemical shifts have been calculated, and some general rules have been withdrawn.