General procedure for the synthesis of methyl 2,3-dichloroisonicotinate from methanol and 2,3-dichloro-pyridine-4-carboxylic acid: to a suspension of 2,3-dichloro-pyridine-4-carboxylic acid (7.7 g, 40 mmol) in dichloromethane (45 mL) was added N,N-dimethylformamide (DMF, 0.1 mL) and oxalyl chloride (17.5 mL, 200 mmol). The reaction mixture was stirred at room temperature for 18 h. The solvent was subsequently removed by distillation under reduced pressure. The resulting residue was azeotroped with toluene to remove residual water, then cooled to 0 °C and dissolved in methanol (135 mL). The mixture was slowly warmed to room temperature and then concentrated again by reduced pressure distillation to give the crude product. The crude product was dissolved in ethyl acetate and the organic layer was washed sequentially with saturated sodium bicarbonate solution, water and brine. The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated to give methyl 2,3-dichloroisonicotinate as a colorless oil, which was crystallized after standing (7.9 g, 96% yield). The structure of the product was confirmed by 1H NMR (CDCl3, 400 MHz): δ 8.38 (d, J = 5.0 Hz, 1H), 7.52 (d, J = 5.0 Hz, 1H), 3.99 (s, 3H).
