Under nitrogen protection, 2-bromothiophene (9.68 mL, 0.1 mol) was slowly added dropwise to a stirred mixture of magnesium scrapings (2.7 g, 0.11 mol) and ether (100 mL), keeping the reaction temperature at 0 °C. Subsequently, the reaction mixture was warmed up to 35 °C with continuous stirring. Next, a solution of dimethyl oxalate (5.9 g, 0.05 mol) in ether (150 mL) was slowly added dropwise over a period of 3 hours. After the dropwise addition was completed, the reaction mixture was heated to reflux (45 °C) and maintained for 45 minutes. Upon completion of the reaction, the mixture was cooled to room temperature and 1.25 M sulfuric acid (150 mL) was added. After stirring for 1 h at room temperature, the organic layer was separated and washed sequentially with dilute aqueous sodium bicarbonate (100 mL) and water (100 mL). The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The resulting solid residue was recrystallized with carbon tetrachloride (1 g / 3 mL) to afford methyl 2,2-dithienyl ethanoate (7.68 g, 30 mmol, 60% yield).
