[Cl:1][C:2]1[CH:11]=[C:10]([CH3:12])[C:9]2[CH2:8][N:7]([C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])[CH2:6][CH2:5][C:4]=2[N:3]=1.[OH2:20]>CCOC(C)=O.[Cl-].[Na+].O.[Ru](Cl)(Cl)Cl>[Cl:1][C:2]1[CH:11]=[C:10]([CH3:12])[C:9]2[C:8](=[O:20])[N:7]([C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])[CH2:6][CH2:5][C:4]=2[N:3]=1To a suspension of ruthenium trichloride (0.141 g, 0.681 mmol) and NaI04 (8.32 g, 38.9 mmol) in H2O (30 mL) at 0° C., a solution of tert-butyl 2-chloro-4-methyl-7,8-dihydro-1,6-naphthyridine-6(5H)-carboxylate (2.75 g, 9.73 mmol) in EtOAc (30 mL) was added. After stirring for 5 min., the reaction mixture was warmed up to rt and stirred. After stirring for 21.5 h, the mixture was diluted with EtOAc and brine. The organic layer was separated, dried over Na2SO4, filtered, and concentrated. The crude was purified by flash column chromatography on 80 g of silica gel (with 25 g pre-column of silica gel; eluent: heptane/EtOAc=100:0 to 70:30) to give tert-butyl 2-chloro-4-methyl-5-oxo-7,8-dihydro-1,6-naphthyridine-6(5H)-carboxylate (2.10 g) as a white solid: 1H NMR (400 MHz, CDCl3) δ ppm 7.15 (s, 1H), 3.98 (t, J=6.32 Hz, 2 H), 3.13 (t, J=6.32 Hz, 2 H), 2.70 (s, 3 H), 1.58 (s, 9 H).
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