Nickel-catalyzed oxidative coupling reactions of two different terminal alkynes using O(2) 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 NiCl(2).6H(2)O/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 O(2) or air as the oxidant. It is the first example using Ni-salt as catalyst by employing air or O(2) as oxidant, which led to efficient heterocoupling of two different alkynes.