General procedure for the synthesis of dimethyl 4-bromophthalate using 5-bromoisobenzofuran-1,3-dione as starting material:(15-1) Synthesis of dimethyl 4-bromophthalate. Methanol (500 mL) was added to 4-bromophthalic anhydride (50.25 g). Subsequently, chlorosulfonic acid (1 mL) was added dropwise to the reaction system. The resulting reaction mixture was heated under reflux conditions overnight. After completion of the reaction, the reaction solution was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: hexane/ethyl acetate system) to afford the target product dimethyl 4-bromophthalate (39.98 g, 66.1% yield) as a colorless oil. The structure of the product was confirmed by 1H-NMR (400 MHz, CDCl3): δ (ppm) 3.90 (3H, s), 3.92 (3H, s), 7.63 (1H, d, J = 8.4 Hz), 7.68 (1H, dd, J = 2.0, 8.4 Hz), 7.84 (1H, d, J = 2.0 Hz).
