Some novel observations on the reaction of 2-hydrazino-3-methylquinoxaline with trifluoromethyl-β-diketones

The reaction of 2-hydrazino-3-methylquinoxaline 1 with trifluoromethyl-β-diketones 2 not only yields the expected 5-trifluoromethyl-5-hydroxy-Δ2-pyrazolines 3a–3f and/or 3-trifluoromethylpyrazoles 4c–4f but also the unexpected products 1,2,4-triazolo[4,3-a]quinoxalines 5a–5f and/or 3(5)-trifluoromethyl-1H-pyrazoles 6c–6f. Furthermore, the acid-catalyzed dehydration of 5-hydroxypyrazolines 3a–3b resulted in the formation of unexpected 5a–5b along with the expected corresponding pyrazoles 7a–7b. These unprecedented observations provide evidence for the existence of equilibrium between the hydroxypyrazoline 3 and its open chain tautomer, ketoimine 9 in the mechanistic path leading to the formation of pyrazoles 7 and triazoles 5.