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Dess-Martin periodinane (DMP, 27.37 g, 64.4 mmol) was added batchwise to a stirred solution of (5-fluoro-6-methoxypyridin-3-yl)methanol (6.8 g, 43.83 mmol) in dichloromethane (DCM, 150 mL) at 0 °C. The reaction mixture was stirred at room temperature for 16 hours. After completion of the reaction, the reaction mixture was filtered through diatomaceous earth and washed with DCM (3 x 50 mL). The combined organic phases were washed sequentially with saturated aqueous NaHCO3 solution (200 mL), water (100 mL) and brine (150 mL), dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure to give the crude product. The crude product was purified by column chromatography (silica gel 60-120 mesh, 0-15% petroleum ether solution of ethyl acetate) to obtain 5-fluoro-6-methoxynicotinaldehyde (6.0 g, 89% yield) as a white solid.

[1] Patent: EP2022793, 2009, A1. Location in patent: Page/Page column 73
[2] Patent: WO2015/158427, 2015, A1. Location in patent: Page/Page column 85
[3] Patent: EP2022793, 2009, A1. Location in patent: Page/Page column 73