Enantioselective Copper-Catalyzed Propargylic Etherification of Propargylic Esters with Phenols Promoted by Inorganic Base Additives

An enantioselective copper-catalyzed propargylic etherification of both aromatic and aliphatic propargylic esters with phenols has been developed, in which the employment of inorganic base additives, in particular cesium carbonate (Cs2CO3), was found to significantly promote not only the reactivity but also the enantioselectivity of the reaction. By using a structurally hindered chiral ketimine P,N,N-ligand, a wide range of optically active propargylic ethers were prepared in high yields and with excellent enantioselectivities (up to 98% ee).