Initially, we focused on developing a scalable and mild dimerization method for the C3 position of tryptophan derivative 4 (Scheme 1A). As mentioned earlier, several methods have been reported for dimerizing the C3 position of tryptophan derivatives. We first attempted the dimerization of 4 using 1.8 equivalent of CoCl(PPh3)3, as reported by Movassaghi et al. Although the desired product 5 was obtained, only 24% isolated yield was achieved on a 50 mg scale. Next, we investigated the use of the Ni catalyst and the dppe ligand, as reported by Oguri et al. Although a trace amount of the desired compound 5 was obtained, the reaction was difficult to reproduce. The low yields observed under the Ni and Co conditions may be attributed to the sensitivity of these conditions to the purity and brand of the reagents and solvents, their hygroscopic nature, and the high sensitivity of the low-valent chemical species to oxygen atmosphere, rendering them challenging to handle. On the other hand, the dimerization using NiI2 and 1,10-phenanthroline ligand, as reported by Peng et al., 6b resulted in the dimerized compound 5 in 38% isolated yield. Although dimerization reactions of 4 using existing methods such as CoCl(PPh3)3 5 and Ni-catalysts 6 are feasible, the delicate nature of the reaction makes adjustment and handling of reagents complicated, and the reproducibility of the desired product is poor. Moreover, in the case of CoCl(PPh3)3, more than one equivalent of the reagent is necessary since the reaction is not catalytic. Additionally, the use of Ni poses challenges due to the instability of its low valence state in the presence of oxygen. Given these limitations, we opted to explore a new, more dependable dimerization reaction that can be executed more effortlessly and economically on a decagram scale. After the screening of conditions, interestingly, we found that the use of a Cp2TiCl2 catalyst was successful in obtaining 5 in 35% isolated yield. The advantage of using a Cp2TiCl2 catalyst is that it is inexpensive, stable in air, does not absorb moisture, and requires no expensive ligands, making it suitable for scalable synthesis. On the other hand, in recent years, radical reactions using zirconium have been vigorously studied due to their mild reaction conditions and low toxicity. Since zirconium has physical properties similar to those of titanium, we predicted the bond dissociation energies (BDE) of Ti-Br and Zr-Br bonds in Cp2TiBr2 and Cp2ZrBr2 using DFT calculations. The Ti-Br bond of Cp2TiBr2 was found to be 79.2 kcal/mol, while the Zr-Br bond of Cp2ZrBr2 was 89.5 kcal/mol. From the DFT calculation, it is evident that the Cp2ZrBr2 catalyst can easily produce radicals from 4 through single electron transfer. Indeed, the Cp2ZrCl2 catalyzed dimerization of 4 gave 5 in 65% isolated yield, which was attributed to the strong bond dissociation energy (BDE) of the Zr-Br bond. It is noteworthy to mention that through meticulous investigations of the reaction conditions, the use of dppe was crucial for this reaction. Subsequently, the reducing agent for this reaction was investigated in detail (Scheme 1A). Fe, Mg, or electrochemical reduction conditions commonly employed for transition metal reduction resulted in meager conversion, and only trace amounts of 5 was obtained. Further investigations revealed that the use of Mn as the reducing agent afforded 5 in 25%. However, the most favorable outcome was achieved when Zn dust was employed as the reducing agent, providing an isolated yield of 65% on a 50 mg scale. The effects of solvent on this were also explored. Solvents such as 2-Me-THF, TBME, hexane, EtOAc, DMA, DMF, 1,4-dioxane, and NMP proved to be ineffective. The dimerized compound 5 was obtained in a yield of 19% when MeCN was used, and in a yield of 37% when DME was employed. Further investigations revealed that THF as the solvent provided the highest yield (65%) of 5.