Next, the influence of ligands was examined. The addition of ligands often accelerates the reaction greatly and is therefore a crucial factor to consider. Consequently, we evaluated several greatly, starting with bipyridine and phenanthroline ligands, but these were not effective. Subsequently, a variety of monodentate and bidentate phosphine ligands (tBu3P, dppf, dppp, dppbz, Ph3P, Cy3P, (4-Me-Ph)3P, (4-OMe-Ph)3P, and dppe) were screened. Among these ligands, dppe (10 mol%) was the most effective ligand (yield of 65%) for this reaction. In fact, without dppe, the yield was 56% on a 50 mg scale. Interestingly, further investigations into the addition of dppe demonstrated that the effect of 10 mol% dppe was particularly significant on the gram and decagram scales. In fact, when 5 was synthesized using Cp2ZrCl2 catalyst and Zn dust without dppe, the yield was as low as 25% on 1 g and 10 g scales, and 5 could not be obtained reproducibly. However, when 10 mol% of dppe was utilized as a ligand, 5 was successfully obtained in isolated yields of 52% and 47% on 1 g and 10 g scales, respectively. Based on these findings, a synthetic route was established for the production of 5 by dimerization over Cp2ZrCl2 catalyst, Zn dust, and dppe in THF, providing the desired compound 5 on a decagram scale with good reproducibility. This dimerization approach can be applied to the synthesis of analogs and potential seed compounds on a decagram scale since it does not require strong acidic conditions or high temperatures and proceeds with mild and inexpensive reagents. The proposed reaction mechanism of this dimerization reaction is described below. Initially, the tetravalent catalyst is reduced by Zn dust to form trivalent Cp2ZrCl. This highly active trivalent Cp2ZrCl captures Br in compound 4 by single electron transfer, forming a strong and stable Zr-Br bond and generating a radical species at the benzylic position. The resulting radical above the benzylic position dimerizes to give the desired compound 5.