Rh(III)-catalyzed double C–H activation of aldehyde hydrazones: a route for functionalized 1H-indazole synthesis

A novel and straightforward strategy for functionalized 1H-indazoles is realized by the Rh(III)-catalyzed double C–H activation and C–H/C–H cross coupling of readily available aldehyde phenylhydrazones. The reaction is scalable and various 1H-indazoles could be afforded in moderate to high yields with good functional-group compatibility. Mechanism experiments and DFT calculations suggest the distinctive Rh(III)-catalyzed C–H/C–H cross coupling reaction underwent a cascade C(aryl)–H bond metalation, C(aldhyde)–H bond insertion and reductive elimination process.