Hydrochloric Acid → Methyl 2-methoxypyridine-3-carboxylate

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반응 단계

Methyl 2-methoxynicotinate was synthesized from ethyl 2-chloronicotinate with sodium methoxide as described in Example 34. A 100 mL dry flask was charged with 2-methylanisole (7.92 g, 65 mmol), acetyl chloride (5.1 mL, 71 mmol), aluminum chloride (9.45 g, 71 mmol) and 40 mL of anhydrous dichloromethane. The reaction mixture was kept at reflux for 2 h, then poured into 15 mL of HCl (3 N) and extracted with 100 mL ether. The organic layer was further washed with sodium bicarbonate to pH 6-7, then further washed with brine and dried over sodium sulfate. The solvent was evaporated and the residue was dried under high vacuum to yield the intermediate (10.0 g, 93.85%). A 100 mL dry flask was charged with methyl 2-methoxynicotinate (2.50 g, 15 mmol), 10 mL anhydrous DMF and NaH (0.9 g, 22.5 mmol, 60% in oil). The intermediate (2.58 g, 15.7 mmol) in 3 mL anhydrous DMF was added and the reaction was stirred for 2 hours. The mixture was poured into 120 mL of water with 3 mL AcOH. The yellow solid was further wash with water and passed through a column (hexane:EtOAc 3:1) to give the methoxy intermediate (3.4 g, 75.7%). A 50 mL flask was charged with the methoxy intermediate (1.0 g, 3.3 mmol) and pyridine hydrogen chloride (4.0 g, 33 mmol) and heated to 190° C. for 3 h. The mixture was poured into a sodium bicarbonate solution and the solid was collected by filtration, washed with EtOAc and MeOH (20 mL each) to give 2-(4-hydroxy-3-methylphenyl)-4H-pyrano[2,3-b]pyridine-4-one (0.58 g, 69.4%). MS (ES) m/z: 254.0 (M+1); Mp. 300-302° C.

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