Direct Synthesis of Benzothienoindoles via Lewis Acid-Catalyzed Annulation of Electrophilic Benzothiophenes

Herein, we report a Lewis acid-catalyzed annulation of electrophilic benzothiophenes, which enables efficient access to benzothiophene-fused indoles. The heteroannulation of electrophilic benzothiophenes with anilines is scalable and proceeds with broad substrate generality, delivering benzothieno[3,2- b ]indoles and allowing systematic π-extension to pentacene- and hexacene-type frameworks. Density functional theory calculations elucidate the Lewis acid’s decisive role in activating the electrophilic annulation pathway, providing mechanistic insight into the process.