Palladium-catalyzed Ullmann-type coupling with zinc in the presence of H2O in liquid carbon dioxide

Carbon dioxide was used not only as a reaction medium but also as a reagent to activate ArCl in the palladium-catalyzed Ullmann-type coupling. In liquid carbon dioxide not only various aromatic iodides and bromides but also aromatic chlorides, non-reactivated substrates in earlier reports, were coupled in moderate to good yields in the presence of Pd/C, zinc and H2O at room temperature overnight.