Step F. Synthesis of 3-bromo-6-methoxy-2-pyridinecarboxaldehyde. A mixture of 3-bromo-2-hydroxymethyl-6-methoxypyridine (3.25 g, 14.9 mmol) and manganese dioxide (9.07 g, 104 mmol) in chloroform (50 mL) was heated to reflux for 18 hours. After completion of the reaction, the reaction mixture was filtered while hot and the filtrate was concentrated. The residue was purified by silica gel column chromatography (eluent: 10% ethyl acetate/hexane) to afford 3-bromo-6-methoxy-2-pyridinecarboxaldehyde (2.55 g, 80% yield). Mass spectrum (ESI): calculated value C7H6BrNO2, 214.96; measured value m/z 218.2 [M + H]+. 1H NMR (CDCl3): δ 10.13 (s, 1H), 7.80 (d, J = 8.7 Hz, 1H), 6.83 (d, J = 8.7 Hz, 1H), 3.99 (s, 3H).
