Direct Synthesis of Benzo[c]carbazoles by Pd-Catalyzed C-H [4+2] Annulation of 3-Arylindoles with External 1,3-Dienes

Herein, we present a regioselective Pd-catalyzed C-H [4 + 2] benzannulation of N-unprotected 3-arylindoles with external readily available 1,3-dienes via an original sequence involving a Pd-catalyzed domino carbopalladation of 1,3-dienes/direct C2-H allylation of an indole ring followed by an oxidation or reduction step. Depending on the nature of the solvent, DCE or CH3CN, two consecutive approaches, oxidative or reductive, have been validated and applied to the design of a novel library of C6 alkyl or (E)-C6-styryl-benzo[c]carbazoles in moderate to good yields.