The reaction between hydrazines and β-dicarbonyl compounds: proposal for a mechanism

Abstract

The reaction between aryl or heteroarylhydrazines with fluorinated β-diketones (CF3COCH2COR) yields a variety of 3-, 5-, and 3,5-trifluoromethylpyrazoles and 5-trifluoromethyl-5-hydroxy-Δ2-pyrazolines. Twenty-one of such compounds have been isolated and identified by 13C and 19F NMR. Together with the results from the literature they provide a comprehensive overview of the reaction. Semi-empirical calculations at the PM3 level have been used to rationalize these results. The outcome that emerges seems to be that the dehydration of a pair of 3,5-dihydroxypyrazolidines kinetically controls the isomer formed.Key words: hydrazines, 1,3-diketones, pyrazolines, pyrazoles, PM3 calculations.