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5-Bromo-3-methyl-thiophene-2-carboxylic acid (example 1.b, 10.0 g, 45.2 mmol) was suspended in 40 mL of thionyl chloride. The mixture was heated at reflux temperature for 1 hour and then cooled to 0° C. with an external ice bath. Cold ethyl alcohol (150 mL) was carefully added, and the solution was heated at reflux temperature for 16 hours. Under reduced pressure, the solution was concentrated to ca. one third of the original volume and then diluted with ethyl acetate and washed successively twice with saturated sodium bicarbonate solution, and once with brine. The organic fractions were dried over anhydrous sodium sulfate and concentrated to 7.9 g of a yellow oil: 1H NMR (CDCl3, 200 MHz): δ=6.87 (s, 1H), 4.34-4.23 (q, 1H, J=7.0 Hz), 2.50 (s, 3H), 1.39-1.32 (t, 3H, J=7.0 Hz).

1. temperatureThe mixture was heated
2. temperatureat reflux temperature for 1 hour
3. temperaturethe solution was heated
4. temperatureat reflux temperature for 16 hours
5. concentrationUnder reduced pressure, the solution was concentrated
6. additiondiluted with ethyl acetate
7. washwashed successively twice with saturated sodium bicarbonate solution
8. dry with materialThe organic fractions were dried over anhydrous sodium sulfate
9. concentrationconcentrated to 7.9 g of a yellow oil