Palladium-Catalyzed ortho- Alkylation of Bromoarenes Enabled by Imidazole-Olefin Ligands

Direct ortho-C–H functionalization of bromoarenes, with retention of the valuable C–Br bond, remains an unsolved challenge despite the broad synthetic utility of these substrates. We report an approach to ortho-alkylation of diverse bromoarenes through Pd-olefin catalysis, employing a synergistic system with a newly designed imidazole-olefin ligand and a bulky phosphine. Mechanistic studies reveal how the imidazole ligand concurrently suppresses unproductive C–C reductive elimination and activates the key palladacycle intermediate toward alkylation through secondary coordination. Notably, these insights guided reaction optimization that reduced the olefin ligand loading while maintaining efficiency. This work establishes a practical route to complex polysubstituted arenes and underscores the power of tailored ligand design in palladium-olefin catalysis.