[C:1]([O:5][C:6]([N:8]1[CH2:17][CH2:16][C:15]2[N+:14]([O-])=[C:13]([Cl:19])[CH:12]=[CH:11][C:10]=2[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[C:20]([O:23]C(=O)C)(=[O:22])[CH3:21]>C(Cl)Cl>[C:20]([O:23][CH:16]1[C:15]2[N:14]=[C:13]([Cl:19])[CH:12]=[CH:11][C:10]=2[CH2:9][N:8]([C:6]([O:5][C:1]([CH3:4])([CH3:3])[CH3:2])=[O:7])[CH2:17]1)(=[O:22])[CH3:21]A solution of 6-(tert-Butoxycarbonyl)-2-chloro-5,6,7,8-tetrahydro-1,6-naphthyridine 1-oxide (150 mg, 0.53 mmol) in acetic anhydride (2.5 mL, 26.3 mmol), was stirred and heated at 70° C. overnight under nitrogen atmosphere. DCM (20 mL) was added to the reaction mixture, and the resulting solution was washed sequentially with water, saturated aqueous NaHCO3 solution and brine, dried over anhydrous MgSO4, and concentrated under vacuum. The residue was purified by flash chromatography on silica gel eluting with 0% to 30% EtOAc in hexane to give the title compound (115 mg, 66.8% yield). 1H NMR (400 MHz, CDCl3) δ ppm 1.51 (9H, s), 2.13 (3H, s), 3.30-3.49 (1H, d, J=12.0 Hz), 4.25-4.40 (1H, m), 4.45-4.55 (1H, d, J=12.0 Hz), 5.20-5.00 (1H, m), 5.73 (1H, br. s), 7.34 (1H, d, J=8.22 Hz), 7.51 (1H, d, J=8.41 Hz) ppm; LC/MS m/z: 327 (M+1).
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