Synthesis
General procedure for the synthesis of 3-chloro-4,5-dihydroxybenzoic acid from 3-chloro-4-hydroxy-5-methoxybenzoic acid:
Step (i): tribromoborane (7.86 mL, 82 mmol) was added dropwise to a stirred solution of 3-chloro-4-hydroxy-5-methoxybenzoic acid (6.61 g, 32.6 mmol) in dichloromethane (50 mL) under nitrogen protection. The reaction mixture was continued to be stirred at 0 °C for 2 h and subsequently poured in batches into ice/brine (250 mL). The aqueous phase was extracted with ethyl acetate (2 x 150 mL) and the combined organic phases were dried over magnesium sulfate and filtered. The solvent was removed by concentration under reduced pressure to give 3-chloro-4,5-dihydroxybenzoic acid (5.11 g, 79% yield). Mass spectrum (electrospray ionization, negative mode) m/z 187 [M-H] ; 1H NMR (400 MHz, DMSO-d) δ: 12.69 (1H, broad single peak), 10.14 (2H, broad single peak), 7.35 (1H, double peak), 7.32 (1H, double peak).
References
[1] Patent: WO2011/27106, 2011, A1. Location in patent: Page/Page column 106-107
[2] Patent: US2012/149737, 2012, A1. Location in patent: Page/Page column 58
[3] Bioorganic and Medicinal Chemistry, 2018, vol. 26, # 4, p. 798 - 814
