2-Aminophenol → 2-Aminobenzoxazole
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[NH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[OH:8].C(OCC)(=O)C.[N:15]#[C:16]Br.[OH-].[Na+]>O>[NH2:15][C:16]1[O:8][C:3]2[CH:4]=[CH:5][CH:6]=[CH:7][C:2]=2[N:1]=1[NH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[OH:8].C(OCC)(=O)C.[N:15]#[C:16]Br.[OH-].[Na+]>O>[NH2:15][C:16]1[O:8][C:3]2[CH:4]=[CH:5][CH:6]=[CH:7][C:2]=2[N:1]=1A mixture of 2.5 g 2-aminophenol (7-1) and 20 ml ethyl acetate was heated to 45° C. 3 g of cyanogen bromide was added to the mixture. The mixture was stirred at 45-50° C. for 12 hours. After cooling to room temperature, 1.5 g of sodium hydroxide in 15 ml of water was added. The organic layer was separated and washed with brine until neutral pH. Toluene (5 ml) was added and the solvent was removed to yield 2.71 g (88%) 2-aminobenzoxazol (7-2). 7.5 ml of chlorosulfonic acid was stirred at room temperature under an inert atmosphere (nitrogen). 5 g of 2-aminobenzoxazol (7-2) was added in small portions. The temperature was kept between 30-60° C. during the addition of 7-2. The mixture was heated to 80° C. for 2 hours. 5.3 g of thionyl chloride was added drop wise, keeping the temperature at 65° C. The mixture was stirred during 2 hours. After cooling to 0° C. 10 ml of ethyl acetate and 10 ml of a solution of sodium carbonate (1N) were added. The organic layer was separated from the water layer and this latter was extracted with ethyl acetate. The combined organic layers were dried over calcium chloride, yielding 7.8 g (90%) of 2-amino-6-chlorosulfonylbenzoxazole (7-3).
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