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Keywords:

  • azoles;
  • C[BOND]H activation;
  • coupling reactions;
  • density functional calculations;
  • reaction mechanisms

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[BOND]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.