Synthesis of Annulated Carbazoles via FeCl3/SnCl4‑Mediated Domino Reaction of Vinyl Ketone Tethered Bromomethylindoles with Arenes and Heteroarenes

Abstract

One pot synthesis of aryl- as well as heteroaryl- annulated carbazoles was achieved from 2/3-bromomethylindole involving Lewis-acid mediated domino reaction with arenes as well as heteroarene via successive Friedel-Crafts intermolecular as well as intramolecular alkylations followed by elimination of acetone. Further, the bis-domino reaction of 2,5-bis-bromomethylpyrrole was also carried out with selected heteroarenes. Additionally, the synthesized thienocarbazole and thienodibenzofuran were successfully utilized for a second-generation domino reaction.

Recent synthetic strategies for the construction of functionalized carbazoles and their heterocyclic motifs enabled by Lewis acids

“…The desired annulated carbazoles were generated in 8b–e 64–70% yields by the cascade annulation reaction of 3-bromomethylindole provided by 2-vinyl ester with xylenes and benzodioxole in the presence of 20 mol% FeCl 3 ( Scheme 12 ). 105 In the same way, napthocarbazole (8f–g) was prepared with yields of 74% and 76%. The proposed Lewis acid mediated annulation mechanism is cited in Schemes 12 and 13 .…”

“…The desired heteroannulated carbazoles 8e–j were obtained by reaction of bromomethylindole with thiophene-, indole-, and pyrrole-based heteroarenes as mentioned in Scheme 14 . 105 …”