Construction of Alkaloid-Type Bis Carbazoles via Pd(II)-Catalyzed C-H Functionalization

We report the construction of unsymmetrical dimeric carbazoles and π-extended bis carbazoles (having an aryl ring spacer) via the C−H functionalization route. Generally, oxidative coupling and traditional cross-coupling reactions have been used to construct bis- and π-extended carbazoles. Natural bis carbazole alkaloids and synthetic dimeric carbazoles are important molecules in medicinal, materials chemistry research. There is scope for developing new synthetic transformations leading to structurally appealing bis carbazoles. The synthesis of symmetrical bis carbazoles via cross-coupling and C−H functionalization is well known in the literature and it is noted that there exist limited reports on the construction of unsymmetrical bis carbazoles via the C−H functionalization route. Accordingly, this paper reveals the Pd(II)-catalyzed bidentate directing group-assisted C−H functionalization as a progressive route for the synthesis of a library of unsymmetrical dimeric carbazoles and π-extended bis carbazoles (connected through an aryl ring spacer).