To a suspension of 4-chloropyridine-2-carboxylic acid (4.5 g, 29.0 mmol) in methylene chloride (120 mL) was added oxalyl chloride (3.0 mL, 1.2 eq) under Ar2. The reaction was cooled to 0° C., and 500 uL of DMF was added. A large amount of gas was generated in situ. The reaction was stirred at room temperature for 1.5 h and then concentrated. Dry MeOH (50 mL) was added to the crude acyl chloride residue. The reaction was stirred at room temperature for 0.5 h, then quenched with NaHCO3 (5%) to neutral, extracted with EtOAc, and washed with brine. The combined organics were dried over MgSO4, filtered, and concentrated in vacuo to give 5.0 g of a crude solid, which was triturated with 5% EtOAc/hexane to give Methyl 4-chloropicolinate as a light yellow solid (4.5 g, 90%).
[1] Patent: US2008/234332, 2008, A1. Location in patent: Page/Page column 22; 25
[2] Patent: CN105175325, 2017, B. Location in patent: Paragraph 0024; 0025
[3] Patent: WO2008/77188, 2008, A1. Location in patent: Page/Page column 28
[4] Patent: US9533973, 2017, B2. Location in patent: Page/Page column 34
[5] Bioorganic and Medicinal Chemistry Letters, 2010, vol. 20, # 8, p. 2512 - 2515
