Step (ii): synthesis of methyl 4-chloro-3-methoxy-5-nitrobenzoate (3)
Methyl 4-hydroxy-3-methoxy-5-nitrobenzoate (2) (4.4 g, 19 mmol) was dissolved in DMF (30 mL) at 0 °C and oxalyl chloride (5.09 mL, 58.1 mmol) was added dropwise. The reaction mixture was stirred at 80 °C for 3 h under the protection of a CaCl2 drying tube. After completion of the reaction, the mixture was cooled to room temperature, slowly poured into ice water (100 mL) and stirred for 15 minutes. The precipitate was collected by filtration and washed sequentially with water and methanol to afford methyl 4-chloro-3-methoxy-5-nitrobenzoate (3) as a yellow solid (3.2 g, 65% yield). The product was characterized by 1H NMR (400 MHz, CDCl3): δ 8.04 (1H, d), 7.77 (1H, d), 4.04 (3H, s), 3.97 (3H, s).
