Our initial efforts in achieving regioselective arylation of Dha-derivative 2 focused on the use of arylthiantrenium salt 1 (For detailed optimization, see Supporting Information). We employed DIPEA as the stoichiometric reductant and eosin Y as a photocatalyst, with the reaction driven by visible light irradiation at a wavelength of 456 nm (Table ). The reaction proceeded efficiently (72% isolated yield) in a solvent mixture of MeCN:HFIP (7:1) at room temperature over 4 hours (Table , Entry 1). Other protic or aprotic polar solvents failed to provide satisfactory conversions (Table , Entries 2 and 3). It became evident that the choice of solvent was critical; variations in the solvent system composition, containing different ratios between MeCN and HFIP, resulted in decreased yields (Table , Entry 4). A control experiment demonstrated the essential role of DIPEA (entry 5). Other potential reductants, including various amines and dihydropyridines, were also tested but failed to effectively produce the target product 3 (Table and). Furthermore, we explored a range of photoorganocatalysts and metal-based photocatalysts, which unfortunately led to less efficient processes (Table and). Gratifyingly, the synthesis of the unnatural amino acid 3 could be smoothly performed in a continuous-flow photoreactor in a significantly reduced reaction time (tR = 20 min) with comparable efficiency (Table , Entry 10).