Synthesis of dihydroindazolo[2,3-f]phenanthridin-5(6H)-ones via Rh(iii)-catalyzed C–H activation of 2-aryl indazoles and annulation with iodonium ylides

Abstract

An efficient synthetic route to indazole-fused dihydrophenanthridinones in excellent to almost quantitative yields under mild reaction conditions was developed. The reaction utilizes the acid-controlled Rh(III)-catalyzed C–H activation of 3-arylindazoles followed by their annulation with readily available hypervalent iodonium ylides. This methodology afforded a wide range of products that could be isolated using only a simple filtration without the need for column chromatography. In addition, the catalytic system can be recycled at least eight times with excellent yields, which may make it amenable to industrial production. Moreover, the photophysical properties of the synthesized dihydroindazolo[2,3-f]phenanthridin-5(6H)-ones indicate that they may have potential applications as new fluorescent materials.