Ligand-Free Suzuki Cross-Coupling Enables Green and Scalable Synthesis of 2,1,3-Benzothiadiazole Derivatives

As a common building block, 2,1,3-benzothiadiazole (BT) is widely used in the synthesis of organic semiconductor materials. However, the conventional synthesis of BT derivatives as key material intermediates typically relies on the Stille cross-coupling reaction. This method requires the use of highly toxic organotin reagents, limiting scalability and industrial applicability. In this work, we report a green and scalable synthetic strategy based on phosphine-ligand-free Pd(OAc)2-catalyzed Suzuki cross-coupling. A stable neopentyl glycol boronate ester intermediate was efficiently prepared via a practical borylation route, avoiding unstable boronic acids and hazardous reagents. Systematic investigation of catalyst, solvent system, base, water content, temperature, and reaction time revealed that Pd(OAc)2 without external phosphine ligands delivers superior catalytic performance. Under the optimized reaction conditions, a series of BT derivatives were successfully synthesized with yields exceeding 90%. Notably, the method enables 100 g scale synthesis of Y6-DA’D with excellent yield and purity. This strategy provides a green, efficient, and scalable alternative to conventional Stille coupling and represents a promising approach for industrial production of BT-based organic semiconductor materials.