Visible-Light-Induced Synthesis of Carbazoles by in Situ Formation of Photosensitizing Intermediate

A visible-light-induced synthesis of N-H carbazoles from easily accessible 2,2′-diaminobiaryls in the absence of any external photosensitizer is reported. The process only requires ^tBuONO and natural resources, visible light, and molecular oxygen for the synthesis of N-H carbazoles. Experimental and computational studies support that the in situ formation of a visible-light-absorbing photosensitizing intermediate, benzocinnoline N-imide, is responsible for the activation of triplet molecular oxygen to singlet oxygen that, in turn, promotes the synthesis of carbazole.