Microwave-assisted aqueous Suzuki cross-coupling reactions

The poly(ethylene glycol) ester of bromo-, iodo-, and triflate-para-substituted benzoates are smoothly cross-coupled with aryl boronic acids (Suzuki reaction) under "ligandless" palladium acetate catalysis in water. The reaction proceeds without organic cosolvent under conventional thermal conditions (70 degrees C, 2 h) and under microwave irradiation (75 W, 2-4 min). The polymeric support remains stable under both reaction conditions. Whereas conventional thermal conditions induced ester cleavage (up to 45%), this side reaction is suppressed when microwave conditions are employed. Aryl nonaflates give fair yields under these conditions. Non-polymer-bound aryl halides form biaryls in good to excellent yields in water/poly(ethylene glycol) mixtures under microwave irradiation (4 min, 75 W).