Synthesis
Ethyl 5-methyl-1H-pyrrole-2-carboxylate (400 mg, 2.61 mmol) was dissolved in a mixed solvent of dioxane/water/ethanol (10 mL/1 mL/2 mL) with reference to the method of Curran, T.; Keaney, M. (J. Org. Chem., 61(25), 1996, 9068-9069). Sodium hydroxide (520 mg, 13 mmol) was added and the reaction was refluxed for 3 hours. After completion of the reaction, the solvent was removed under reduced pressure. The crude product was dissolved in water and extracted with dichloromethane (DCM). The aqueous phase was adjusted to pH 1 with 1N hydrochloric acid and the organic and aqueous phases were separated. The organic phase was dried with anhydrous sodium sulfate and concentrated under reduced pressure to give the crude 5-methyl-1H-pyrrole-2-carboxylic acid, which can be used in the next reaction without further purification. Yield: quantitative; LCMS (retention time): 2.51 min (Method D); MS (ES+) m/z: 126.03.
References
[1] Patent: WO2006/123257, 2006, A2. Location in patent: Page/Page column 57-58
[2] Tetrahedron Letters, 2003, vol. 44, # 1, p. 61 - 63
[3] Chemistry - A European Journal, 2017, vol. 23, # 14, p. 3300 - 3320
[4] ACS Medicinal Chemistry Letters, 2015, vol. 6, # 5, p. 553 - 557
[5] Annali di Chimica (Rome, Italy), 1956, vol. 46, p. 847,854
