Regioselective Synthesis of 1-Bromo-1,4-dienes by Free-Radical-Mediated Bromoallylation of Activated Acetylenes

The free-radical-mediated bromoallylation of acetylenes proceeded efficiently in the presence of V-65 (2,2-azobis(2,4-dimethylvaleronitrile)) as the radical initiator. The regioselective reaction, which yields 1-bromo-2-substituted 1,4-dienes, is complementary to the Pd-catalyzed bromoallylation reaction previously reported by Kaneda. The products of the free-radical-mediated bromoallylation of acetylenes could be converted into a variety of substituted dienes by subsequent Pd-catalyzed reactions.