“On-water” one-pot four-component synthesis of novel 1H-furo[2,3-c]pyrazole-4-amine derivatives

A catalyst-free, simple and green protocol has been accomplished for the synthesis of novel 1H-furo[2,3-c]pyrazole-4-amines in a one-pot four-component domino reaction involving hydrazines, ethyl acetoacetate, aromatic amines and phenylglyoxal monohydrate in water. The protocol presented herein describes in situ generated pyrazolone as intermediate reactants with phenylglyoxal monohydrate in a Knoevenagel condensation followed by a Michael addition of amine, intramolecular cyclization, dehydration and the resulting to the title compound. It was observed that in this protocol bis(pyrazole-5-ols) are formed with amines bearing strong electron withdrawing groups under similar reaction conditions instead of the expected products. The reaction merits the use of water as solvent, no additive catalyst, easy workup, easy purification of products by non-chromatography and provides high yield of products with good purity.