Step 13b. 6-Bromo-2-methylnicotinic aldehyde (Compound 1102, 1.4 g, 6.7 mmol) was taken as raw material and dissolved in acetone (20 mL) at 0 °C and Jones reagent (2.67 M, 5.2 ml) was added slowly with stirring. The reaction mixture was gradually warmed up to room temperature and stirring was continued for 30 min. After completion of the reaction, the pH of the reaction solution was adjusted to 5-6 with saturated NaHCO3 solution. the reaction mixture was extracted with ethyl acetate, the organic layers were combined, washed with brine, dried over anhydrous sodium sulfate and concentrated. The crude product was purified by silica gel column chromatography with the eluent ethyl acetate/hexane (1:8) to afford 6-bromo-2-methylnicotinic acid (Compound 1103, 1.0 g, 66% yield) as a white solid.1H NMR (400 MHz, CDCl3): δ 2.87 (s, 3H), 7.46 (d, J=8.4 Hz, 1H), 8.15 (d, J= 8.4Hz, 1H).
