[F:1][C:2]1[CH:3]=[N+:4]([O-:16])[C:5]2[CH:6]=[CH:7][C:8](=[O:15])[N:9]([CH2:12][CH:13]=C)[C:10]=2[CH:11]=1.O.I([O-])(=O)(=O)=[O:19].[Na+]>O1CCOCC1.[Os](=O)(=O)(=O)=O>[F:1][C:2]1[CH:11]=[C:10]2[C:5]([CH:6]=[CH:7][C:8](=[O:15])[N:9]2[CH2:12][CH:13]=[O:19])=[N+:4]([O-:16])[CH:3]=17-Fluoro-1-(2-propen-1-yl)-1,5-naphthyridin-2(1H)-one 5-oxide (340 mg, 1.544 mmol) was stirred in 1,4-dioxane (16 mL) and water (8 mL) was added, followed by sodium periodate (990 mg, 2.3 eq.) and osmium tetroxide (1 mL of 4% aqueous solution). The mixture was stirred at room temperature for 3 hours. The solvents were evaporated under reduced pressure (water bath temperature 30° C.) to a volume of ca. 10 mL, and the residue was extracted with 20% methanol in DCM (v:v, 3×50 mL). The combined organic extracts were dried over anhydrous sodium sulphate, filtered and evaporated under reduced pressure to give (7-fluoro-5-oxido-2-oxo-1,5-naphthyridin-1(2H)-yl)acetaldehyde largely as its methyl hemiacetal) as a tan foam (327 mg). LCMS showed major peaks for the aldehyde hydrate (32%) and the methyl hemiacetal (64%).
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