Reaction of hydrazinoquinolines with trifluoromethyl-beta-diketones: Structural and mechanistic studies

Reaction of 2-hydrazino-4-methylquinoline with a series of trifluoromethyl-beta-diketones gives 3-substituted-5-hydroxy-1-(4-methylquinolin-2-yl)-5-trifluoromethyl-4,5-dihydropyrazoles and, in some cases, 5-substituted-1-(4-methylquinolin-2-yl)depending on the substitution of the diketone. Dehydration of the hydroxydihydropyrazoles can be effected with sulphuric acid in acetic acid to give the regioisomeric 3-substituted-1-(4-methylquinolin-2-yl)-5-trifluoromethylpyrazoles. In contrast, the reaction of two 4-hydrazinoquinolines with 1,1,1-trifluoropentane-2,4-dione afforded a different isolable intermediate, the corresponding hydrazone formed at the 4-carbonyl. Dehydration gave the 1-(substituted-quinolin-4-yl)-3-methyl-5-trifluoromethylpyrazoles. The regioisomeric identity of the pyrazoles was established using F-19 NMR. (C) Elsevier Science S.A.