Synthesis of 1,3-Diynes via Palladium-Catalyzed Reaction of 1,1-Dibromo-1-alkenes

[reaction: see text] Both symmetric and unsymmetric 1,3-diynes were prepared from the palladium-catalyzed reaction of 1,1-dibromo-1-alkenes. The formation of symmetric 1,3-diynes 2 (homocoupling) was catalyzed by a weak ligand, tris(2-furyl)phosphine (TFP), and the addition of catalytic amount of CuI accelerated the reaction. The synthesis of unsymmetric 1,3-diynes 4 (the Sonogashira reaction) required a highly electron rich tris(4-methoxyphenyl)phosphine as the ligand, and CuI promotes the formation of byproduct 1,1-diynyl-1-alkenes 5.