Regioselective C-H Sulfonylation of 2H-Indazoles by Electrosynthesis.

This study reveals a transition-metal- and external oxidant-free electrochemical method for the C3-H sulfonylation of biologically diverse 2H-indazoles at room temperature and under ambient air. Using various sulfonyl hydrazides as the sulfonyl precursor, a series of sulfonylated indazole derivatives containing a broad spectrum of functional groups were synthesized in up to 92% yield. Mechanistic studies suggest a precedented radical pathway is operating in the electrochemical process.