Iron promoted C3-H nitration of 2H-indazole: direct access to 3-nitro-2H-indazoles.

An efficient C3-H functionalization of indazole has been demonstrated. Notably, this method involves chelation-free radical C-H nitration on 2H-indazole. The radical mechanism was confirmed by control experiments and quantum chemical calculations. The synthetic utility has been proven by the synthesis of bio-relevant benzimidazoindazoles via reductive cyclization.