1-Piperidinecarboxaldehyde → 5-Bromo-2-fluoro-3-pyridinecarboxaldehyde

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A solution of lithium di-iso-propylamine (5 mL, 35 mmol) in anhydrous THF (40 mL) was cooled to −78° C. under nitrogen and n-butyl lithium (2.5 M in hexanes, 12 mL, 30 mmol) was added. The mixture was then stirred at −78° C. for 15 min before 5-bromo-2-fluoro-pyridine (5 g, 28 mmol) was added. The resulting mixture was then stirred at −78° C. for 90 min. N-formylpiperidine (4 mL, 36 mmol) was added very rapidly to the suspension at −78° C. and the mixture stirred vigorously for 60 sec. The reaction was immediately quenched by the addition of a 10% (w/v) aqueous solution of citric acid. The mixture was warmed to room temperature and distributed between water and dichloromethane. The aqueous phase was extracted three times with dichloromethane and the organic phases were combined, dried over sodium sulfate, filtered and concentrated. Crystallization of the crude product from cyclohexane afforded 5-bromo-2-fluoro-pyridine-3-carbaldehyde (2.993 g, 52% yield) as pale beige flaky crystals. 1H-NMR (500 MHz, d6-DMSO) δ10.07 (s, 1H), 8.70 (dd, 1H), 8.55 (dd, 1H). MS: m/z 236, 238 [MNa+], 204, 206 [MH+], 176, 178 [MH—CO+].

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