Green Synthesis of Spiro[indoline‐3,4′‐pyrazolo[3,4‐b][1,6]naphthyridine]‐2,5′(1′H)‐diones Catalyzed by TsOH in Ionic Liquids.

A three-component reaction of isatin, 3-methyl-1-phenyl-1H-pyrazol-5-amine, and piperidine-2,4-dione was treated in ionic liquids catalyzed by TsOH and provided an efficient and green method for the synthesis of spiro[indoline-3,4′-pyrazolo[3, 4-b][1,6]naphthyridine]-2,5′(1′H)-dione derivatives in high yields.