Synthesis of Pyrazolo[1,2‐a]indazoles via Iridium(III)‐Catalyzed [4+1] Spiroannulation Reaction of Pyrazolidinones and 2‐Diazo‐1,3‐indandiones

A novel protocol for synthesizing pyrazolo[1,2‑a]indazoles from readily available pyrazolidinones and 2‐diazo‐1,3‐indandiones through the Ir(III)‐catalyzed C─H bond activation and intramolecular spiroannulation reaction has been described. This approach provides pyrazolo[1,2‑a]indazoles in moderate to good yields, in which C─C/C─N bonds formed in one pot. In addition, 2‐diazo‐1,3‐indandiones act as C1 synthons under these extremely mild reactions. Generally, this method exhibits high efficiency and broad functional group compatibility. What's more, studies on the activity of selected products against human cancer cells (HeLa) demonstrate their further application in medicinal chemistry.