Nickel-Catalyzed Oxidative Coupling Reactions of Two Different Terminal Alkynes Using O2 as the Oxidant at Room Temperature: Facile Syntheses of Unsymmetric 1,3-Diynes

Two different terminal alkynes now can be coupled together in the presence of NiCl2·6H2O/CuI by using an excess of one of the terminal alkyne substrates. The new method employed 20 mol % TMEDA as the ligand and environmentally benign O2 or air as the oxidant. It is the first example using Ni-salt as catalyst by employing air or O2 as oxidant, which led to efficient heterocoupling of two different alkynes.