Mechanism Selection for Regiocontrol in Base‐Assisted, Palladium‐Catalysed Direct CH Coupling with Halides: First Approach for Oxazole‐ and Thiazole‐4‐Carboxylates

Abstract Both base‐assisted non‐concerted metallation–deprotonation (nCMD) and concerted metallation–deprotonation (CMD) have been identified as two potent operating mechanisms in palladium‐catalysed direct CH coupling of oxazole and thiazole‐4‐carboxylate esters with halides through base‐ and solvent‐effect experiments. Novel C2‐ and C5‐selective CMD direct arylation procedures in oxazole‐ and thiazole‐4‐carboxylate series were then designed by controlling the balance between electronic and steric factors. Notably, charge interactions between the palladium catalyst and substrate were identified as a parameter for controlling selectivity and reducing the impact of steric factors in the CMD reaction.