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

Abstract

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.