An E-factor minimized solvent-free protocol for the preparation of 4,5-dihydro-5-(trifluoromethyl)-1H-pyrazoles

摘要

The efficient synthesis of 4,5-dihydro-1H-pyr-azoles from the reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones [CF3C(0)CH=C(R~1)(OR), where R = Me, Et and R~1 = H, Me, Et, Pr, i-Bu, Ph, 4-Me-C6H4, 4-F-C6H4, 4-Cl-C6H4, fur-2-yl, Naphth-2-yl, biphenyl-4-yl] and ethyl 3-hydrazino-3-oxopropionate [NH2NHC(O)CH2C(O)OEt] is reported. The products were obtained in good yields (72-87%). Two protocols were developed: (1) conventional thermal heating using EtOH as solvent and under solvent-free conditions, and (2) a microwave-assisted method using EtOH as solvent and under solvent-free conditions. The E-factor was determined for all protocols, and the results showed that the microwave-assisted method under solvent-free conditions results in a greener process.