Synthesis
Step 2: Preparation of 4-hydroxy-3-methoxy-2-nitrobenzaldehyde; A mixture of 4-formyl-2-methoxy-3-nitrophenyl acetate (438 g, 1.8 mol) and potassium carbonate (506 g, 3.7 mol) in methanol (4000 mL) was stirred for 16 hours at room temperature. Upon completion of the reaction, the reaction mixture was concentrated under reduced pressure to give a viscous oily substance. The oily substance was dissolved in water, acidified to pH<7 with 2N hydrochloric acid solution and subsequently extracted with ethyl acetate (EtOAc). The organic layer was washed with saturated brine, dried over anhydrous magnesium sulfate (MgSO4) and filtered. The filtrate was concentrated to 1/3 of the original volume under reduced pressure, a solid was precipitated, filtered and dried over air to afford the target product 4-hydroxy-3-methoxy-2-nitrobenzaldehyde (317 g, 88% yield). The product was characterized by 1H NMR (DMSO-d6): δ 9.69 (s, 1H), 7.68 (d, 1H), 7.19 (d, 1H), 3.82 (s, 3H).
References
[1] Journal of Heterocyclic Chemistry, 2015, vol. 52, # 5, p. 1406 - 1410
[2] Patent: WO2004/29055, 2004, A1. Location in patent: Page 51
[3] Journal of Chemical Research, Miniprint, 1990, # 12, p. 2831 - 2867
[4] Patent: WO2016/71380, 2016, A1. Location in patent: Page/Page column 43
[5] Patent: WO2008/70150, 2008, A1. Location in patent: Page/Page column 65-66
