A direct synthesis method towards spirocyclic indazole derivatives via Rh(III)-catalyzed C–H activation and spiroannulation

A rhodium(III)-catalyzed [4 + 1] spiroannulation of N-aryl phthalazine-diones (pyridazine-diones) with diazo compounds to construct spirocyclic indazole derivatives with diverse structures is described. The corresponding spiroannulation products were obtained in moderate to good yields. This reaction can be formally viewed as the result of C–H activation, carbene insertion and a nucleophilic addition process. Additionally, this method features high atom-economy and high functional group tolerance.