Copper-Catalyzed Nondecarboxylative Cross Coupling of Alkenyltrifluoroborate Salts with Carboxylic Acids or Carboxylates: Synthesis of Enol Esters

A mild copper-catalyzed Chan-Lam-Evans type cross-coupling reaction for the regioselective and stereospecific preparation of (E)- or (Z)-enol esters is described. The method couples carboxylate salts or carboxylic acids with potassium alkenyltrifluoroborate salts In the presence of catalytic CuBr and DMAP with 4 angstrom molecular sieves under O-2 at 60 degrees C. Overall, this method demonstrates carboxylic acids as suitable reaction partners for nondecarboxylative copper-catalyzed cross-couplings to form C-O bonds in an Ullmann-like reaction.