N1C=CC=CC=1.[OH:7][C:8]1[CH:17]=[C:16]2[C:11]([C:12](=[O:18])[NH:13][CH:14]=[N:15]2)=[C:10]([O:19][CH:20]([CH3:22])[CH3:21])[CH:9]=1.[C:23](OC(=O)C)(=[O:25])[CH3:24]>O>[C:23]([O:7][C:8]1[CH:17]=[C:16]2[C:11]([C:12](=[O:18])[NH:13][CH:14]=[N:15]2)=[C:10]([O:19][CH:20]([CH3:22])[CH3:21])[CH:9]=1)(=[O:25])[CH3:24]Pyridine (0.18 ml, 1.5 mmol) was added to a suspension of 7-hydroxy-5-isopropoxyquinazolin-4(3H)-one (3.3 g, 15 mmol) in acetic anhydride (10 ml, 75 mmol) and the mixture was stirred at 75° C. for 45 minutes. The mixture was evaporated under reduced pressure and the residue obtained was stirred in water (50 ml) at 75° C. for 1 hour and then cooled to ambient temperature and filtered to afford 5-isopropoxy-4-oxo-3,4-dihydroquinazolin-7-yl acetate (2.6 g, 65% yield) as a white solid:
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