Copper-catalyzed Ullmann-type synthesis of diaryl ethers assisted by salicylaldimine ligands

A series of salicylaldimine ligands were designed to promote the copper-catalyzed Ullmann crosscoupling reaction. After a screening process, 2-((2-isopropylphenylimino)methyl)phenol was found to serve as a good supporting ligand for this reaction. Employing this Schiff-base ligand as a new supporting ligand, the copper-catalyzed coupling reactions of aryl bromides and aryl iodides with various phenols successfully proceeded in good yields under mild conditions. Various diaryl ethers were obtained with excellent yields in dioxane in the presence of K3PO4 and a catalytic amount of copper(I) salt.