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A mixture of 4-(2-thienyl)butyric acid (4.25 g, 25.0 mmol) and 3 mL of concentrated sulfuric acid in 25 mL of methanol is heated at reflux for 2 hours. The reaction mixture is cooled to room temperature and partitioned between ethyl acetate and saturated aqueous sodium carbonate solution. The organic layer is separated and passed through a short pad of silica gel. The filtrate is concentrated and purified by flash column chromatography eluting with 1:5 ethyl acetate:hexane to provide 4.02 g of 4-thiophen-2-yl-butyric acid methyl ester as a yellow oil, 1H NMR (DMSO-d6) δ 1.85 (quintet, J=7 Hz, 2H), 2.35 (t, J=7 Hz, 2H), 2.81 (t, J=7 Hz, 2H), 3.59 (s, 3H), 6.84 (m, 1H), 6.95 (m, 1H), 7.32 (dd, J=5, 1 Hz, 1H); MS 185.0 (M+H)+.

1. temperatureis heated
2. temperatureat reflux for 2 hours
3. custompartitioned between ethyl acetate and saturated aqueous sodium carbonate solution
4. customThe organic layer is separated
5. concentrationThe filtrate is concentrated
6. custompurified by flash column chromatography
7. washeluting with 1:5 ethyl acetate