A 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.
