One-Pot Synthesis of 1,4-Dihydropyrano[2,3-c]pyrazoles Catalyzed by Basic Ionic Liquids

A series of 1,4-dihydropyrano[2,3-c]pyrazoles were synthesized via four-component one-pot reaction of aromatic aldehyde, malononitrile, ethyl benzoylacetate and hydrazine or hydrazinobenzene. 1-Butyl-3-methyl imidazolium hydroxide ([bmim]OH) was used as basic ionic liquid catalyst. The effect of catalyst, reaction temperature, catalyst amount and solvent on the yield were investigated. The optimum reaction condition was determined and the possible mechanism was proposed. Besides, the catalyst could be recovered conveniently and reused for at least four times without evident loss of activity. The products were identified by H-1 NMR, IR, MS techniques and elemental analysis. The present methodology offers several advantages such as milder reaction condition, shorter reaction time, excellent yield and environmental friendliness.