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

The reaction between aryl or heteroarylhydrazines with fluorinated beta-dik etones (CF3COCH2COR) yields a variety of 3-, 5-, and 3,5-trifluoromethylpyr azoles and 5-trifluoromethyl-5-hydroxy-Delta(2)-pyrazolines. Twenty-one of such compounds have been isolated and identified by C-13 and F-19 NMR. Toge ther with the results from the literature they provide a comprehensive over view of the reaction. Semi-empirical calculations at the PM3 level have bee n used to rationalize these results. The outcome that emerges seems to be t hat the dehydration of a pair of 3,5-dihydroxypyrazolidines kinetically con trols the isomer formed.