5-Amino-2-methyl pyridine (2.8 g, 25.9 mmol) was added to a mixture of water (15 mL) and cone. HCl (7 mL) and cooled to 0°C. NaNO2 (3.5 g, 51.8 mmol) was added portion-wise with stirring over 10 min whilst keeping the reaction temperature between -5℃ and O℃. After stirring for 10 min 60 % w/w HPF6 (14 mL) was added dropwise with cooling, at which point a precipitate formed. This was filtered, washed with cold water and diethyl ether and dried. The solid was then heated slowly to 100℃; the reaction being very exothermic. After 5 min a dark red oily material formed which was then cooled to r.t. The oil was basifed with dilute sodium hydroxide to pH ~10 and extracted with dichloromethane. The combined organics were dried over sodium sulfate, filtered and evaporated in vacuo. The residue was purified by column chromatography over neutral alumina using 20 % dichloromethane-petroleum ether to yield 5-fluoro-2- methyl pyridine (1.57 g, 55%) as an oil.
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[5] Patent: WO2018/15410, 2018, A1. Location in patent: Paragraph 0365-0368
