Ultrasound-assisted synthesis of 1,5-disubstituted pyrazoles via HFIP-mediated cascade cyclization of enaminones with aryl hydrazine

A simple and efficient metal-free strategy has been developed for the synthesis of 1,5-disubstituted pyrazole derivatives by using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) medium and ultrasound irradiation. The condensation reactions of β-enaminone and aromatic hydrazine have taken place at room temperature with the assistance of sonication. The protocol provides rapid access to various N-aryl substituted pyrazole compounds with excellent functional group tolerance and yields. Notably, the eco-friendly and cost-effective method allows the conversion within a short time and under mild conditions.