[C:1](Cl)(=O)C(Cl)=O.[Cl:7][C:8]1[CH:13]=[C:12]([C:14]([OH:16])=[O:15])[CH:11]=[C:10]([O:17][CH2:18][C:19]2[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=2)[N:9]=1>CN(C=O)C.C(Cl)(Cl)Cl>[Cl:7][C:8]1[CH:13]=[C:12]([C:14]([O:16][CH3:1])=[O:15])[CH:11]=[C:10]([O:17][CH2:18][C:19]2[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=2)[N:9]=1With cooling with ice, oxalyl chloride (5.8 mL) and DMF (3 drops) were added to a CHCl3 (40 mL) solution of 2-chloro-6-benzyloxypyridine-4-carboxylic acid, and stirred at that temperature for 1 hour. DMF (3 drops) was added to it, and stirred overnight at room temperature, then oxalyl chloride (2.9 mL) and DMF (3 drops) were added to it, and stirred at room temperature for 3 hours. The solvent was evaporated away, CHCl3-MeOH was added to the residue, and stirred at room temperature for 30 minutes. Sodium bicarbonate water was added to the reaction solution, extracted with chloroform, and the organic layer was washed with water, saturated sodium bicarbonate water and saturated saline water, and dried with anhydrous sodium sulfate. This was filtered, concentrated under reduced pressure, and the residue was purified through silica gel column chromatography (hexane/ethyl acetate) to obtain the title compound as a yellow oil.
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