Aerobic Oxidative Coupling of 2-naphthols by Simple Copper Salts: A Highly Efficient Catalytic System in the Absence of Ligand or Carrier

Abstract
A ligand-free or carrier-free copper salt system that catalysed aerobic oxidative coupling of 2-naphthols has been established. 1,1′-Bi-2-naphthols were afforded in excellent yields in methanol in the presence of 5 mol % copper (| or ||) salts. The coupling reaction could also be performed very well in aqueous solvents.