COCN[C:5]([C:7]1[C:12]([F:13])=[CH:11][C:10]([Br:14])=[CH:9][N:8]=1)=[O:6].CC(C[AlH]CC(C)C)C>C1COCC1>[F:13][C:12]1[C:7]([CH:5]=[O:6])=[N:8][CH:9]=[C:10]([Br:14])[CH:11]=1A solution of 3-fluoro-5-bromopyridine carboxylic acid methoxymethylamide (630 mg, 2.4 mmol) in dry THF (12 mL) was cooled to −50° C. and DIBAL (1M in THF; 2.8 mL, 2.8 mmol) was added over 15 min maintaining the temperature below −50° C. The reaction was stirred at −50° C. for 2 h. An additional portion of and DIBAL (1M in THF; 0.25 mL, 0.25 mmol) was added and the reaction mixture was allowed to warm slowly to −10° C. over 2 h. The reaction was quenched by the dropwise addition of water (5 mL) and the THF was removed in vacuo and a dilute solution of Rochelle's salt was added. The aqueous was extracted with EtOAc (×3) and the combined organics dried (MgSO4) and concentrated in vacuo. Purification by column chromatography (gradient: 10%-90% EtOAc in petroleum ether 40-60c) yielded 3-fluoro-5-bromopyridine-2-carbaldehyde as a yellow solid.
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