General procedure for the preparation of methyl 5-bromo-2-(methylthio)pyrimidine-4-carboxylate: 5-bromo-2-(methylthio)pyrimidine-4-carboxylic acid (7.64 g, 30.7 mmol) was dissolved in methanol (60 mL). Sulfuric acid (2 mL) was added to the solution and the mixture was subsequently heated to reflux for 24 hours. Upon completion of the reaction, the mixture was poured into ice water and extracted with dichloromethane (DCM). The organic phase was washed with saturated aqueous sodium bicarbonate solution, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target compound methyl 5-bromo-2-(methylthio)pyrimidine-4-carboxylate (6.42 g, 80% yield). The product was characterized by 1H NMR (500 MHz, CDCl3): δ 8.72 (s, 1H), 4.01 (s, 3H), 2.58 (s, 3H).LCMS (ESI) analysis showed a retention time of Rt = 2.35 min and a molecular ion peak 263 [M + H]+.
[1] Patent: WO2014/37750, 2014, A1. Location in patent: Paragraph 00149; 0046-0050
[2] Patent: WO2015/128676, 2015, A1. Location in patent: Page/Page column 117-118
[3] Journal of Medicinal Chemistry, 2017, vol. 60, # 6, p. 2215 - 2226
[4] Patent: WO2017/221100, 2017, A1. Location in patent: Paragraph 00284
[5] Patent: EP3305785, 2018, A1. Location in patent: Paragraph 0167; 0168