General procedure for the synthesis of 6-bromo-2,3-difluorobenzaldehyde from 3,4-difluorobromobenzene and N,N-dimethylformamide: Aryl bromide (1.0 eq.) was dissolved in anhydrous THF (0.2 M) and the reaction mixture was cooled to -78 °C under nitrogen protection. LDA (2.0 M in THF, 1.1 eq.) was added dropwise over 15 min. Stirring was continued for 20 min after addition. DMF (1.2 eq.) was then added and stirred at -78 °C for 15 min. Glacial acetic acid (4.0 eq.) was added, followed immediately by water (12 times the volume of glacial acetic acid) and the reaction mixture was slowly warmed to room temperature. The phases were separated and the aqueous phase was extracted twice with ethyl acetate. The combined organic layers were washed sequentially with dilute aqueous HCl, water and brine. The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated. The resulting residue was purified by silica gel column chromatography with the eluent being a hexane solution of 0 to 5% ethyl acetate to give 6-bromo-2,3-difluorobenzaldehyde (83% yield) as a yellow oil.1H NMR (CDCl3) δ: 7.31 (t, J = 1.4 Hz, 1H), 7.45 (ddd, J = 9.0, 4.1, 1.9 Hz, 1H), 7.29 (td, J = 9.2, 8.0 Hz, 1H).
