Organometallic catalyst studies have been continuously studied to increase the reactivity of organic reactions and selectively synthesize only one isomer. In this thesis, we have discussed the reaction of palladium-catalyzed regioselective dimerization of cinnamyl bromide. Because the allyl structure has two reactive sites, structure isomers are synthesized as byproducts in the two allyl-allyl coupling reactions. However, the palladium catalyst and the bidentate ligand shows high reactivity and regioselectivity in dimerization of cinnamyl bromide. As a result, anti $\gamma$,$\gamma$-regioselective dimers could be selectively synthesized.