Synthesis of 1,3-diynes via palladium-catalyzed reaction of 1,1-dibromo-1-alkenes

Both symmetric and unsymmetric 1,3-diynes were prepared from the palladium-catalyzed reaction of 1,l-dibromo-l-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 Cul 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 Cul promotes the formation of byproduct 1,1-diynyl-1-alkenes 5.