Synthesis
b) General procedure for the synthesis of methyl 4-bromothiophene-2-carboxylate: 6.02 g (29.1 mmol) of 4-bromothiophene-2-carboxylic acid (prepared as in the previous procedure) was dissolved in 100 mL of anhydrous methanol under nitrogen protection and cooled to -20 °C. The reaction was completed by the addition of 2.55 mL (34.9 mmol) of thionyl chloride. 2.55 mL (34.9 mmol) of thionyl chloride was slowly added dropwise at a controlled acceleration rate to maintain the reaction temperature below -5 °C (dropwise addition was completed in about 8-10 min). After completion of the dropwise addition, the reaction mixture was stirred at room temperature for 1 hour, followed by refluxing for 8 hours. Upon completion of the reaction, the mixture was cooled and concentrated in vacuum. The resulting 6.7 g of light amber oily product was purified by passing through a 150 g silica gel column, eluting with about 600 mL of dichloromethane (discarding the first 120 mL of the eluate which contained small amounts of impurities). Vacuum concentration gave the title compound, methyl 4-bromothiophene-2-carboxylate, as a colorless oil (6.11 g, 95% yield).1H-NMR (300 MHz, CDCl3) δ 7.69 (d, 1H, J = 1.5 Hz), 7.45 (d, 1H, J = 1.5 Hz), 3.90 (s, 3H).
References
[1] Patent: US2004/72871, 2004, A1. Location in patent: Page/Page column 29
[2] Patent: US2002/37915, 2002, A1
[3] Patent: US6291514, 2001, B1
[4] Patent: US2004/9995, 2004, A1
[5] Archiv der Pharmazie, 1998, vol. 331, # 12, p. 405 - 411
