CuCl-catalyzed green oxidative alkyne homocoupling without palladium, ligands and bases

CuCl-catalyzed green oxidative homocoupling of terminal alkynes produces symmetrical 1,4-disubstituted 1,3-diynes in good to excellent yields, using air as an environmentally friendly oxidant and the occurrence of water as exclusive byproduct in the whole process, and eliminating the need for ligands, bases, oxidants and expensive palladium catalysts.