A general and mild Ullmann-type synthesis of diaryl ethers

An efficient method for the synthesis of diaryl ethers under particularly mild conditions is described. Inexpensive ligands were found to greatly accelerate the Ullmann-type coupling of aryl bromides or iodides with phenols. A series of diaryl ethers were obtained with excellent yields in acetonitrile in the presence Of Cs2CO3 and catalytic copper(l) oxide. The reaction tolerates substrates with unfavorable substitution patterns, such as sterically hindered coupling partners or electron-rich aryl halides.