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.