Dihydro derivatives of pyrazolo[3,4-b]pyridine-, pyrazolo[1,5-a]pyrimidine-, and [1,2,4]triazolo[ 1,5-a]pyrimidinecarboxylates have been prepared by cyclocondensation of beta-aroylacrylates with 5-aminopyrazoles and 3-amino-1,2,4-triazole. Heating dihydro[1,2,4]triazolo[1,5-a]pyrimidine-7-carboxylates with hydrazine hydrate led to recyclization of the pyrimidine ring to form 6-arylpyridazin-3(2H)-ones.