[Cl:1][C:2]1[CH:3]=[C:4]([C:10]([N:12]2[CH2:17][CH2:16][O:15][C:14]3[CH:18]=[N:19][CH:20]=[CH:21][C:13]2=3)=[O:11])[CH:5]=[CH:6][C:7]=1[O:8]C.B(Br)(Br)Br.C(=O)([O-])O.[Na+].Cl>ClCCl>[Cl:1][C:2]1[CH:3]=[C:4]([C:10]([N:12]2[CH2:17][CH2:16][O:15][C:14]3[CH:18]=[N:19][CH:20]=[CH:21][C:13]2=3)=[O:11])[CH:5]=[CH:6][C:7]=1[OH:8]In a 10 ml flask, (3-chloro-4-methoxy-phenyl)-(2,3-dihydro-pyrido[3,4-b][1,4]oxazin-1-yl)-methanone (134 mg, 0.441 mmol) was dissolved in dichloromethane (5 ml), and the mixture was cooled to 0□. 1.0M Boron tribromide dissolved in dichloromethane (2.2 ml, 2.2 mmol) was added thereto and stirred at room temperature for 16 hours. After neutralizing with saturated solution of sodium hydrogen carbonate to pH 8 to 9, the mixture was adjusted to pH 6 again by using 1N hydrochloric acid and extracted with dichloromethane. The combined organic layer was washed with saturated saline solution and dried over anhydrous sodium sulfate (Na2SO4), filtered and evaporated under reduced pressure. The residue was purified by column chromatography on silica eluting with a solvent of methanol:dichloromethane=1:20. The fractions containing the product were collected and evaporated to obtain the target compound 34 as white solid (65 mg, 50.9%).
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