[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)=[N+:4]([O-:16])[CH:3]=1.[NH:17]1[CH2:22][CH2:21][CH:20]([NH:23][C:24](=[O:30])[O:25][C:26]([CH3:29])([CH3:28])[CH3:27])[CH2:19][CH2:18]1.[BH-](OC(C)=O)(OC(C)=O)OC(C)=O.[Na+].C([O-])(O)=O.[Na+]>C(Cl)(Cl)Cl.CO.C(Cl)Cl>[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][CH2:13][N:17]2[CH2:18][CH2:19][CH:20]([NH:23][C:24](=[O:30])[O:25][C:26]([CH3:28])([CH3:27])[CH3:29])[CH2:21][CH2:22]2)=[N+:4]([O-:16])[CH:3]=1A mixture of (7-fluoro-5-oxido-2-oxo-1,5-naphthyridin-1(2H)-yl)acetaldehyde (as the methyl hemiacetal) (327 mg, 1.286 mmol) and 1,1-dimethylethyl 4-piperidinylcarbamate (283 mg, 1.1 eq.) in chloroform:methanol (9:1 v:v) (5 ml) was stirred for 2 h before addition of NaBH(OAc)3 (481 mg, 2 eq.). The reaction was stirred for 0.5 h before addition of sat. aq NaHCO3 (5 ml). The reaction was then diluted with DCM (80 mL) and the organic phase was separated using a hydrophobic frit. The aqueous phase was extracted with DCM (2×50 mL) The combined organic extracts were dried, evaporated and the crude residue purified by chromatography on silica gel using a 0-20% (2M NH3 in MeOH)/DCM gradient to provide the desired compound (345 mg, 66%) as a tan foam.
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