Synthesis of the Carbazole Scaffold Directly from 2-Aminobiphenyl by Means of Tandem C-H Activation and C-N Bond Formation

An efficient method for the synthesis of the carbazole scaffold was designed and investigated. The method was developed to produce substituted carbazoles by an intramolecular combination of a free amine group and an arene. The steps of the method involved tandem Pd-catalyzed C-H activation and intramolecular C-N bond formation. The method showed good functional group tolerance, and substituent(s) could be on either of the two rings or on both of the two rings of the 2-aminobiphenyl substrate. After ring closure, the reduced Pd catalyst was oxidized to Pd-II by hydrogen peroxide. The novel method was also demonstrated to operate excellently with the corresponding 2-N-acetylaminobiphenyls.