One-pot access to tetrahydrobenzo[c]carbazoles from simple ketones by using O2 as an oxidant.

An effective and operationally simple one-pot Brønsted acid catalyzed cascade method is demonstrated for the synthesis of diversely functionalized carbazole frameworks starting from protecting group free 2-alkenyl indoles. The employment of easily available unactivated ketones as annulating partners, mostly unexplored for the synthesis of carbazoles, is the major highlight of this protocol. This protocol is step- and atom-economical, uses molecular oxygen as the green oxidant, and gives water as the only by-product and is amenable to different functional groups. Moreover, gram-scale synthesis and downstream modification of the obtained products demonstrate the synthetic applicability of this protocol.