One‐pot Three‐component Synthesis of Spiro[pyrazolo[3,4‐b]pyridine‐4,3′‐indoline] Derivatives Catalyzed by Melamine Trisulfonic Acid

Novel spiropyrazolo3,4‐b]pyridine‐4,3′‐indoline] derivatives were prepared by the three‐component reaction of isatins 3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐amine and Meldrum's acid in the presence of a catalytic amount of melamine trisulfonic acid. This protocol provides a simple one‐step procedure with the advantages of easy work‐up, mild reaction conditions and environmentally benign.