Palladium-Catalyzed Arylation and Alkylation of 3,5-Diphenylisoxazole with Boronic Acids via C−H Activation

A method for stoichiometric C−H activation of 3,5-diphenylisoxazole (1) using Pd(OAc)₂ as a reagent in acetic acid leading to the isoxazole palladacycle I was described. Ortho aryl- and alkyl-substituted 3,5-diphenylisoxazoles 3a−f and 5a−i were synthesized by the reaction of I with various boronic acids 2a−f and 4a−i, respectively. p-Benzoquinone was found to be the best oxidant and 1,4-dioxane the best solvent for the transmetalation−reductive-elimination step of I with boronic acids.