[CH3:1][C@H:2]1[N:15]2[C:6]([CH2:7][O:8][C:9]3[C:14]2=[CH:13][C:12]([N+:16]([O-])=O)=[CH:11][CH:10]=3)=[N:5][NH:4][C:3]1=[O:19].[Cl-].[NH4+]>CO.C1COCC1.[Zn]>[NH2:16][C:12]1[CH:13]=[C:14]2[C:9](=[CH:10][CH:11]=1)[O:8][CH2:7][C:6]1[N:15]2[C@H:2]([CH3:1])[C:3](=[O:19])[NH:4][N:5]=1To a solution of (R)-4-methyl-6-nitro-2,10-dihydro-9-oxa-1,2,4a-triaza-phenanthren-3-one (50 g, 191 mmol) and ammonium chloride (102 g, 1907 mmol) in MeOH (700 mL) and THF (700 mL) was added zinc powder (125 g, 1907 mmol) in portions. After addition, the reaction mixture was stirred at 50° C. for 16 h. The reaction mixture was cooled to ambient temperature and filtered. The filter cake was washed with hot MeOH (3×1 L) and the combined organic phase was concentrated in vacuo. The residue was washed with THF (3×500 mL) and the combined organic phase was concentrated to give the crude (R)-6-amino-4-methyl-2,10-dihydro-9-oxa-1,2,4a-triaza-phenanthren-3-one (50 g, 215 mmol, containing residual NH4Cl), which was used in the next step without further purification. 1H NMR (CDCl3, 400 MHz): δ 6.68 (d, J=8.4 Hz, 1H), 6.43 (d, J=2.4 Hz, 1H), 6.16 (dd, J=2.4, 8.4 Hz, 1H), 4.83 (br. s., 1H), 4.56-4.52 (m, 1H), 4.47-4.39 (m, 2H), 1.31 (d, J=6.5 Hz, 3H). LCMS (Table 1, Method 3) Rt=0.803 min; MS m/z: 233 [M+H]+.
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