Gold-Catalyzed Chemoselective Dearomative Ring-Opening Modes of Indoles

A gold-catalyzed dearomative cyclization of indoles with ynone-nitriles assisted by a Lewis or a Brønsted acid has been developed, which provides an efficient route to 4-azafluorenones via an unexpected indole ring-opening process. The key strategy involves the attack of an iminyl intermediate to the indoleninium species at its highly electrophilic C2 position, with both intermediates being generated spontaneously during the dearomatization process. By varying the gold catalyst and acid additives, the 1+1 and 2+1 component reactions can be achieved selectively.