Melamine-modified Chitosan Materials: An Efficient and Recyclable Bifunctional Organocatalyst for Green Synthesis of Densely Functionalized Bioactive Dihydropyrano[2,3-c]pyrazole and Benzylpyrazolyl Coumarin Derivatives

An environmentally benign protocol for diversity-oriented synthesis of functionalized bioactive dihydropyrano[2,3-c]pyrazole and benzylpyrazolyl coumarin derivatives has been investigated by the reaction of aryl aldehydes, ethyl acetoacetate, hydrazine derivatives, malononitrile and 4-hydroxycoumarin in the presence of melamine-modified chitosan (Cs-Pr-Me) materials as a reusable bifunctional organocatalyst. The Cs-Pr-Me materials were properly characterized by the Fourier transform infrared (FTIR) spectroscopy, CHN elemental analysis, thermal gravimetric (TGA) and derivative thermogravimetric (DTG) analysis, field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) spectroscopy. The remarkable advantages of this green protocol are high to quantitative yields of the desired products, short reaction times, wide scope, simple work-up procedure and low loading of a transition metal-free catalyst. An additional advantage of this bio-based organocatalyst is the ability to separate and recycle it easily from the reaction mixture with minimal effort in subsequent runs without significant loss of its catalytic activity.