l-Proline-catalyzed three-component domino reactions for the synthesis of highly functionalized pyrazolo[3,4-b]pyridines

A series of novel N,3-dimethyl-5-nitro-1-aryl-1H-pyrazolo[3,4-b]pyridin-6-amines was obtained in good yields from the domino reactions of N-methyl-1-(methylthio)-2-nitroprop-1-en-1-amine, aromatic aldehydes, and 3-methyl-1-aryl-1H-pyrazol-5-amines in ethanol in the presence of green catalyst, l-proline. This transformation involves the formation of two C–C and one C–N bonds leading to the creation of a six-membered ring in a one-pot operation.