The effect of pressurized carbon dioxide on the cyclocondensation reaction between 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones and hydrazines

Abstract

The synthesis of 1-unsubstituted and 1-phenyl-5-trifluoromethylpyrazoles from the reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones [CF 3 C(O)CH=C(R 1 )OR, where R = Me, Et and R 1 = H, Me, Ph] with hydrazines [NH 2 NHR 2 , where R 2 = H, Ph] in pressurized carbon dioxide is reported for the first time. Reaction conditions such as pressure, temperature and time were evaluated. The methodology developed herein was suitable to synthesize products in moderate to excellent yields (60 % -96 %) and short reaction times (15 -45 min).

Unsaturated polyfluoroalkyl ketones in the synthesis of nitrogen-bearing heterocycles

“…Recently, the successful efforts of synthesis of pyrazoles were applied in ionic liquids, [40][41][42] combined with microwave irradiation [41][42][43][44][45][46] or in supercritical CO 2 used as organic solvent substitute. 47 The application of microwave irradiation provides not only decreasing of the reaction time (from several hours to several minutes compared to conventional heating) but yield increase of target heterocycles as well (including nitrophenyl-substituted hydrazines) (Table 1, entries 8, 11, 13). The type of heterocycle also depends on the irradiation rate: dihydropyrazoles are formed at 200 W whereas at 300 W the formation of pyrazoles was only observed (Table 1, entry 18).…”

“…Pyrazoles were recently prepared under solvent free conditions. 43,47 This approach attractive from both economical and ecological point of view turned out to be very effective. For instance, mono-substituted b-methoxy-CF 3 -enone and its analogues, bearing alkyl (Me) or aryl (Ph) substituents, react with phenylhydrazine, heated in supercritical carbon dioxide, to form 5-triuoromethyl-1H-pyrazoles (Table 1, entry 3).…”