Cl.[S:2]1[C:10]2[C:5](=[N:6][C:7]([C:11]([OH:13])=[O:12])=[CH:8][CH:9]=2)[CH:4]=[CH:3]1.[CH3:14]O>>[S:2]1[C:10]2[C:5](=[N:6][C:7]([C:11]([O:13][CH3:14])=[O:12])=[CH:8][CH:9]=2)[CH:4]=[CH:3]1To a solution of HCl (10%) in MeOH (10 mL) was added thieno[3,2-b]pyridine-5-carboxylic acid (1.0 g, 5.6 mmol, from Step 2, Example 1) and the mixture heated to reflux for 2 hr. After cooling to r.t., half the solvent was removed by evaporation and the remainder was partitioned between EtOAc and H2O. Solid NaHCO3 was added until the system remained basic. Separation, drying, and evaporation of the organic layer afforded 0.75 g (70%) of methyl thieno[3,2-b]pyridine-5-carboxylate.
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