[O:1]1[C:5]2=[N:6][CH:7]=[C:8]([C:10]([OH:12])=O)[CH:9]=[C:4]2[CH:3]=[CH:2]1.C(Cl)(=O)C(Cl)=O.[CH2:19]([NH:21][CH2:22][CH3:23])[CH3:20]>C(Cl)Cl.CN(C)C=O>[CH2:19]([N:21]([CH2:22][CH3:23])[C:10]([C:8]1[CH:9]=[C:4]2[CH:3]=[CH:2][O:1][C:5]2=[N:6][CH:7]=1)=[O:12])[CH3:20]To a suspension of furo[2,3-b]pyridine-5-carboxylic acid (3.30 g, 20.2 mmol) in methylene chloride (80 mL), under a nitrogen atmosphere at room temperature, was added oxalyl chloride (4.2 mL, 48 mmol) and then four drops of dimethylformamide. The reaction mixture was stirred until gas evolution ceased (4-5 hours) and a clear solution resulted. This solution was evaporated in vacuo and the excess oxalyl chloride chased by evaporation with benzene. The residue was dissolved in chloroform (50 mL) and diethylamine (5.2 mL, 50 mmol) was added carefully. After 0.5 hours, the chloroform solution was washed with dilute hydrochloric acid, filtered through a pad of charcoal and evaporated to give crude product (5.49 g). This oil was distilled under vacuum to give purified product (3.62 g, 82% yield), bp: 168°-170° C./1.6 mmHg.
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