CC(C)(C)C([NH:5][C:6]1[C:19]([C:20]([O:22][CH3:23])=[O:21])=[C:18]2[C:9]([C:10]3[CH:11]=[CH:12][N:13]=[N:14][C:15]=3[CH2:16][O:17]2)=[CH:8][CH:7]=1)=O>CO.S(=O)(=O)(O)O>[NH2:5][C:6]1[C:19]([C:20]([O:22][CH3:23])=[O:21])=[C:18]2[C:9]([C:10]3[CH:11]=[CH:12][N:13]=[N:14][C:15]=3[CH2:16][O:17]2)=[CH:8][CH:7]=1A solution of methyl 7-(2,2-dimethylpropionylamino)-10H-9-oxa-1,2-diazaphenanthrene-8-carboxylate (Intermediate 7, 0.702 g) in methanol (50 mL) and sulphuric acid (4 mL) was stirred and heated at reflux for 16 hours. After cooling, the solution was evaporated in vacuo and the residue was partitioned between ethyl acetate and water. The mixture was basified with 5M sodium hydroxide, then stirred and heated until all the solid had dissolved. The layers were separated and the aqueous layer was extracted six times with ethyl acetate. The combined extracts were dried (Na2SO4), filtered and the filtrate was evaporated in vacuo. The residue was triturated with DCM and the solid was collected by filtration to give methyl 7-amino-10H-9-oxa-1,2-diazaphenanthrene-8-carboxylate (0.264 g) as a yellow solid.
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