(E) Preparation of 2-chloro-5-methoxynicotinonitrile: To a flame-dried flask under nitrogen atmosphere, triphenylphosphine oxide (12.0 g, 0.04 mol) and dichloromethane (50 mL) were added, and the mixture was cooled to 0°C-4°C. Subsequently, a solution of trifluoromethanesulfonic anhydride (6.75 mL, 0.04 mol) in dichloromethane (80 mL) was added dropwise. After the dropwise addition, stirring of the reaction mixture was continued for 15 minutes. Next, 2-chloro-5-methoxynicotinamide (8.0 g, 0.04 mol) was added in batches over 15 minutes. The reaction mixture was gradually warmed to room temperature and stirred overnight. After completion of the reaction, the mixture was poured into saturated sodium carbonate solution and extracted with chloroform (2×). The organic phases were combined, concentrated and the residue was purified by silica gel column chromatography using chloroform as eluent to give 6.2 g (86% yield) of 2-chloro-5-methoxynicotinonitrile. The product was characterized by 1H NMR (CDCl3): δ 3.9 (3H, s), 7.5 (1H, d, J = 3 Hz), 8.3 (1H, d, J = 3 Hz); IR spectra (nujol): 2250 cm-1.
