Condensation of 5 (3)-amino-3 (5)-arylpyrazoles with 4-hydroxy-6-methylpyran-2-one leads to 5, 7-dimethyl-2-arylpyrazolo [1, 5-a] pyrimidines, 5-alkoxycarbonylmethyl-7-methyl-2- arylpyrazolo [1, 5-a] pyrimidines and their isomeric 7-alkoxycarbonylmethyl-5-methyl-2- arylpyrazolo [1, 5-a] pyrimidines. These compounds result from competitive reactions and from different cyclization pathways. Structure and mechanism of formation of these new ...