Internal Oxidant-Triggered Aerobic Oxygenation and Cyclization of Indoles under Copper Catalysis

A concise synthesis of pyrazolo[1,5-a]indole derivatives by copper-catalyzed aerobic oxygenation and cyclization of indoles with oxime acetates is described. This protocol represents an elegant example of N-1, C-2, and C-3 tri-functionalization of indoles in one-pot. Mechanistic studies indicate the reaction proceeds through a radical procedure. Oximes as an internal oxidant have been demonstrated to be a driver to initiate aerobic oxidation, which provides a new oxidative pattern for C-H functionalization even with high atom- and step-economy.