Copper‐Catalyzed Cascade Thiolation‐Cyclization of o ‐Bromochalcones With Ethyl Thioglycolate: Access to 3‐Styryl Benzo[ b ]thiophenes

A copper‐catalyzed regioselective thiolation of o ‐bromochalcones with ethyl thioglycolate has been developed for constructing ethyl ( E )‐3‐styrylbenzo[ b ]thiophene‐2‐carboxylates in good to excellent yields (up to 84%) with broad substrate scope and good functional‐group tolerance. This approach highlights the versatility of the methodology, providing a diverse series of 3‐styryl and π ‐conjugated benzo[ b ]thiophenes (>20 examples). Structural confirmation of this novel chemical framework was achieved through a detailed 2D NMR analysis. The transformation proceeds through copper‐catalyzed C─S bond formation, followed by intramolecular condensation and cyclization. Gram‐scale synthesis and late‐stage modification further validate the scalability of this method and its value for synthetic diversification. Overall, this straightforward and regioselective approach offers a practical route for synthesizing structurally diverse ethyl ( E )‐3‐styrylbenzo[ b ]thiophene‐2‐carboxylate derivatives.