Acid-Promoted Domino Access to Substituted Benzo[b]carbazoles

Herein, a straightforward Bro̷nsted acids-promoted domino pathway to build substituted benzo[b]carbazoles has been described from easily accessible ortho-formyl (or ortho-acyl) cinnamate esters and indoles. Noticeably, the protocol was amenable to protecting group-free indoles. Notably, this methodology is based on a single-pot regioselective construction of two new C-C bonds and aromatization sequences under mild and metal-free reaction conditions. The mechanistic studies suggested the initial formation of bis-indole substituted intermediate via a dual aromatic substitution with two indole molecules at the carbonyl carbon of ortho-formyl (or ortho-acyl) cinnamate ester followed by intramolecular cyclization and aromatization with exclusion of a second indole molecule. Besides, the efficacy of this approach was also illustrated by scale-up and derivatization reactions, including the photophysical properties study.