Oxidative Coupling of Carbazoles: A Substituent-Governed Regioselectivity Profile

Oxidative
C–C coupling of carbazoles possessing various
substituents is demonstrated in the presence of organic (metal-free)
recyclable oxidants, such as DDQ or CA/H+, for accessing
bicarbazole regioisomers. Differently substituted carbazoles are examined
to showcase regioselective discrimination (3,3′- versus 1,3′-bicarbazoles)
and preferences based on sterics and electronics in oxidative coupling.
Finally, a mechanism that involves the carbazole radical cation has
been traced (evidenced) and proposed on the basis of the UV–vis–NIR
absorption and EPR spectroscopy results. This study underlines the
strategic chemical preparation of a series of bicarbazoles in an efficient
manner.