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Methyl 3-amino-2-thiophenecarboxylate (3.14 g, 20.0 mmol) was dissolved in pyridine (20 mL) and acetyl chloride (1.5 mL, 21 mmol) was added slowly and dropwise under ice bath cooling conditions. The reaction mixture was stirred at room temperature for 3 hours, then cooled again in an ice bath and supplemented with acetyl chloride (0.3 mL, 4 mmol). Stirring was continued at room temperature for 1.5 h. Upon completion of the reaction, the solvent was removed by concentration under reduced pressure. The resulting solid product was suspended and washed with water to give the final methyl 3-acetylaminothiophene-2-carboxylate (3.80 g, 19.1 mmol, 96% yield).

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