The effect of added CUI on the kinetics of a typical Stille coupling was studied. With triphenylphosphine as Pd ligand, cocatalytic Cu (1) salts can yield a> lOO-fold rate increase over the traditional Stille conditions, but little effect was displayed when CUI was used in conjunction with a sofi ligand, such as triphenylarsine. NMR studies suggest that CUI is an excellent scavenger for free ligand and, since strong ligands in solution are known to ...