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Synthesis of Dihydropyrano[2,3-c]pyrazoles Using Carboxymethyl Cellulose as a Recyclable Catalyst

The synthesis of dihydropyrano[2,3- c ]pyrazoles continues to be an object of attention among organic chemists, due to their diverse bioactivity profiles, which include action as therapeutic agents. 1 The compounds are potential inhibitors of human Chk1 kinase, 2 and they have anticancer, 3 molluscicidal 4 and antimicrobial 5 properties. There are numerous approaches for synthesizing these valuable compounds using such catalysts as theophylline, 6 ZrO 2 nanoparticles, 7 choline chloride/urea deep eutectic mixtures, 8 caffeine, 9 molecular sieves, 10 meglumine, 11 CAPB, 12 L-proline/KF-alumina, 13 lipase ANL, 14 Na 2 eosin Y, 15 bovine serum albumin, 16 b -cyclodextrin, 17 morpholine tri-flate, 18 TPSPPTNM, 19 [Dabco-H][AcO] 20 and DABCO. 21 Each of these methods has its own value, but finding environmentally friendly and greener approaches for synthesizing dihydropyrano[2,3- c ]pyrazoles will be increasingly important. In this vein, our own work has been aimed at developing green synthetic processes. 22,23 We here report a solvent-free environmentally friendly synthesis of the title compounds through the use of carboxymethyl cellulose (CMC) (Figure 1) as a green, recyclable, and biodegradable catalyst (Scheme 1). 24,25 The reaction is envisioned as taking place through the tandem Knoevenagel-Michael cyclocondensation of ethyl acetoacetate, hydrazine hydrate, aryl aldehydes and malononitrile using CMC as catalyst. The catalytic activity of CMC for the process was first examined in a model system