1,3-Dipolarcycloaddition of nitrileimines with α,β-unsaturated five- and six-membered lactones, thiolactones and lactams gave ring-fusedpyrazoles. Regioisomeric mixtures have been obtained with the 5-substituted pyrazole as the major cycloadduct. Only with the five-membered lactone the major product was the 4-acyl derivative. Computational studies, the use of the topological analysis of the Fukui