“…[6][7][8] Among them, direct oxidative cyclization reactions have emerged as one of the most powerful approaches for carbazole synthesis because preactivation of the substrates can be avoided, in addition to the atom-and step-economy of the reaction. [9][10][11][12][13] Ever since Åkermark et al reported the oxidative cyclization of diphenylamine via a two C-H bond activation process using a stoichiometric amount of palladium acetate, 14) the palladium-catalyzed intramolecular oxidative coupling reaction of diarylamines in the presence of various oxidants such as cupric acetate, [15][16][17] tert-butyl hydroperoxide, 18) silver oxide, 19) and oxygen [20][21][22] has been further developed and the potential synthetic utility of this type of transformation has been significantly improved (Chart 1A). In recent years, the photochemical cyclization 23,24) and molybdenum pentachloride mediated 25) homogeneous reactions of triarylamines and diarylamines under mild conditions have been successfully developed.…”