An Efficient and Eco‐Friendly One‐Pot Synthesis of Pyrazolopyridines Mediated by Choline Chloride/Urea Eutectic Mixture

In this contribution several choline chloride‐based deep eutectic solvents were evaluated as novel reaction media for the multicomponent one‐pot synthesis of pyrazolopyridine derivatives. It was found that the reaction between hydrazines, ethyl acetoacetate, ammonium acetate and aldehydes or ketones is efficiently catalyzed by the eutectic mixture choline chloride/urea yielding a wide variety of tetrahydrodipyrazolopyridine derivatives in good to excellent yields. In addition, the low melting mixture was reused in four cycles without observing a detrimental catalytic activity. A convenient approach for the synthesis of pyrazolopyridines using the choline chloride/urea deep eutectic solvent is described. The developed methodology offers several advantages over the reported procedures like the use of an economic, environmentally friendly and reusable solvent in combination with a simple operational procedure and high yields of products.