Step a) Synthesis of methyl 2-(bromomethyl)-3-nitrobenzoate: 21 g (109 mmol) of methyl 2-methyl-3-nitrobenzoate was dissolved in 300 mL of carbon tetrachloride, heated to reflux with continuous stirring. Subsequently, 23 g (130 mmol, 1.2 eq.) of N-bromosuccinimide and 1.8 g (11 mmol, 0.1 eq.) of 2,2'-azobis-2-methylpropanenitrile were sequentially added to the reaction system. Maintaining reflux conditions, the reaction mixture was stirred overnight. After completion of the reaction, it was cooled to room temperature, the reaction mixture was diluted with dichloromethane and washed with water several times. The organic phase was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give the crude product. Yield: 31 g (quantitative). The product was analyzed by high performance liquid chromatography (HPLC, Method 12) with a retention time (Rt) of 4.33 min; the mass spectrum (ESI positive ion mode) showed m/z = 273 [M + H]+; 1H-NMR (300 MHz, DMSO-d6) data were as follows: δ= 8.16 (d, 1H), 8.11 (d, 1H), 7.74 (t, 1H), and 5.03 (s, 2H), 3.92 (s, 3H).
