Synthesis of Dibenzo[a,c]phenazines through Brønsted Acid-Catalyzed Skeletal Editing of 2-Arylindoles with 1,2-Diaminoarenes.

Abstract

Herein, Brønsted acid-catalyzed skeletal editing of 2-arylindoles with 1,2-diaminoarenes in the presence of tert-butyl nitrite (TBN) has been developed to prepare various dibenzo[a,c]phenazines in moderate to good yields. Mechanistic studies revealed that this skeletal editing of indoles involved a sequence of nitrosation, condensation, cyclization, diazotization, and intramolecular electrophilic substitution over five steps in one pot. More importantly, the dibenzo[a,c]phenazine could be easily obtained on a gram scale and novel π-extended polyaromatic dibenzo[a,c]phenazine derivatives were obtained by further transformations that show the fluorescence emission wavelength in near-infrared region I (NIR-I). This example represents the first skeletal editing of indoles through a ring-opening and denitrogenation strategy.