Ethyl Thioglycolate → 4-Isobutyl-5-methylthiophene-2-carboxylic acid

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Reaction Steps

Sodium (10.7 g, 467 mmol) is dissolved in ethanol (500 mL) and the resulting solution is diluted with THF (100 mL) before mercapto-acetic acid ethyl ester (33.7 g, 280 mmol) dissolved in THF (70 mL) is slowly added at 5° C. The mixture is stirred at rt for 1 h before a solution of 3-chloro-2-isobutyl-but-2-enal (30 g, 187 mmol) in THF (100 mL) is slowly added at 8° C. The resulting yellow suspension is stirred at rt for 16 h. The reaction mixture is diluted with diethyl ether (500 mL) and is washed with dilute aq. NaOCl solution, followed by aq. 1N HCl and water. The organic extract is dried over MgSO4, filtered and evaporated. The remaining orange oil is dissolved in ethanol (150 mL) and 2N aq. LiOH (50 mL) is added. The mixture is stirred for 16 h at 50° C., acidified with 2 N aq. HCl and extracted with EA. The organic extract is dried over MgSO4, filtered and evaporated. The crude product is recrystallized from EA/heptane to give 4-isobutyl-5-methyl-thiophene-2-carboxylic acid (10.5 g) as colourless crystals; LC-MS: tR=0.92 min, [M+1+CH3CN]=240.16; 1H NMR (CDCl3): δ 7.59 (s, 1H), 2.40-2.37 (m, 5H), 1.84 (hept, J=7.0 Hz, 1H), 0.90 (d, J=7.0 Hz, 6H).

Provenance & Evidence