B(Br)(Br)Br.[Cl:5][C:6]1[C:7]2[N:16]=[C:15]([C:17]3[CH:22]=[C:21]([CH3:23])[C:20]([O:24]C)=[C:19]([CH3:26])[CH:18]=3)[O:14][C:8]=2[N:9]=[C:10]([S:12][CH3:13])[N:11]=1.C(=O)(O)[O-].[Na+]>ClCCl>[Cl:5][C:6]1[C:7]2[N:16]=[C:15]([C:17]3[CH:22]=[C:21]([CH3:23])[C:20]([OH:24])=[C:19]([CH3:26])[CH:18]=3)[O:14][C:8]=2[N:9]=[C:10]([S:12][CH3:13])[N:11]=1At −20° C., 5.30 g of boron tribromide were added dropwise with stirring to a solution of 6.72 g of 7-chloro-2-(4-methoxy-3,5-dimethylphenyl)-5-methylsulfanyloxazolo[5,4-d]pyrimidine in 140 ml of dichloromethane. The reaction mixture was allowed to warm to room temperature and stirred for 2 hours. With ice cooling, another 1.33 g of boron tribromide were then added dropwise. After a further 2 hours, the reaction was once more cooled to −20° C., and sat. aqueous sodium bicarbonate solution was carefully added dropwise. The phases were separated at room temperature. The organic phase was washed with water, dried over sodium sulfate, filtered and concentrated under reduced pressure. The residue was triturated with diisopropyl ether, filtered off with suction and air-dried. This gave 6.20 g (96%) of the title compound, which was reacted further without any further purification.
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