Pyrrolidine-Catalyzed Four-Component One-Pot Synthesis of Dihydropyrano[2,3- C]Pyrazole Derivatives

Pyrrolidine was used as a catalyst for the simple, convenient, and highly efficient synthesis of dihydropyrano[2,3-c]pyrazole derivatives. Four-component one-pot reactions of β-ketoester, hydrazine, ethyl glyoxalate or ethyl pyruvate, and malononitrile in ethanol under reflux conditions led to excellent yields of 79%-94%.