AbstractThe synthesis of pyrazoles 13–24 has been accomplished by treatment of 3‐benzylchromones 1–5, 3‐benzylflavones 6–12 and their 4‐thio analogues 25–29 with hydrazine hydrate in hot pyridine. A plausible reaction mechanism for the formation of pyrazoles 13–24 is discussed. A 1H NMR study in [D6]DMSO allowed the presence of both pyrazole annular tautomers to be observed, due to the presence of intramolecular hydrogen bonds in each tautomer (OH‐‐N and NH‐‐O). GIAO/B3LYP/6‐311++G** calculations were carried out on some model pyrazoles to provide a theoretical basis for the NMR experimental observations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)