反应详情

To a solution of 5-chloro-4-methoxy-2-vinyl-pyridine (435 mg, 2.57 mmol) in acetone (20 mL) and water (20 mL), KMnO4 (2.03 g, 12.8 mmol) is added. The mixture is stirred at rt for 15 h before it is filtered through a glass-filter pad. The filtrate is evaporated and dried to give 5-chloro-4-methoxy-pyridine-2-carboxylic acid (987 mg) as potassium salt containing water in the form of a white solid; LC-MS: tR=0.45 min, [M+1]+=187.91. This material is dissolved in ethanol (20 mL) and H2SO4 (4 mL) is added. The mixture is stirred at 80° C. for 18 h. The solvent is evaporated and the residue is dissolved in EA (150 mL) and washed with sat. aq. NaHCO3 solution and water. The org. extract is dried over MgSO4, filtered and concentrated. The crude product is purified on prep. TLC plates using heptane:EA 1:1 to give 5-chloro-4-methoxy-pyridine-2-carboxylic acid ethyl ester (350 mg) as a pale yellow oil; LC-MS: tR=0.81 min, [M+1]+=215.92; 1H NMR (D6-DMSO): δ 1.34 (t, J=7.3 Hz, 3H), 4.05 (s, 3H), 4.37 (q, J=7.0 Hz, 2H), 7.75 (s, 1H), 8.61 (m, 1H).

1. filtrationis filtered through a glass-filter pad
2. customThe filtrate is evaporated
3. customdried