5-Formylthiophene-3-carboxylic acid → 5-(Hydroxymethyl)thiophene-3-carboxylic acid

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A solution of sodium borohydride (12.5 g, 330 mmol) in water (150 mL) and ethanol (100 mL) at 0° C. is charged with 5-formyl-thiophene-3-carboxylic acid (20.6 g, 132 mmol) in one portion. After warming to room temperature and stirring for 4 h, the mixture is diluted with water and the resulting precipitate vacuum filtered. The filtrate is concentrated and the resulting aqueous solution is washed with ether (2×). The aq layer is acidified with concentrated HCl and extracted with ether (3×). The combined ether extracts are dried over Na2SO4, filtered and concentrated in vacuo to give 5-hydroxymethyl-thiophene-3-carboxylic acid (14.6, 70%) as a white solid; mp 149° C.; 1H NMR (DMSO-d6, 300 MHz) δ 12.60 (s, 1 H), 8.10 (s, 1 H), 7.20 (s, 1 H), 5.52 (t, J=6.0 Hz, 1 H), 4.60 (s, 2 H).

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