B(Br)(Br)Br.O1C2C=CC=CC=2C=N1.[CH2:14]([O:16][C:17]1[C:21]2[CH:22]=[CH:23][C:24]([O:26]C)=[CH:25][C:20]=2[O:19][N:18]=1)[CH3:15].C([O-])(O)=O.[Na+].[Na+].[Cl-]>ClCCl.O.CCCCCC.C(OCC)(=O)C>[CH2:14]([O:16][C:17]1[C:21]2[CH:22]=[CH:23][C:24]([OH:26])=[CH:25][C:20]=2[O:19][N:18]=1)[CH3:15]
Boron tribromide (1.0M solution in dichloromethane; 1.39 ml, 1.39 mmol) was added to a stirred, −78° cooled solution of benzisoxazole from part (c) (179 mg, 928 μmol) in dichloromethane (4 ml) under an argon atmosphere. The reaction mixture was gradually warmed to room temperature over approx. 2 hours, and stirred overnight. Tlc (silica, 2:1 hexane/ethyl acetate) showed new polar material as well as unreacted starting material. The reaction was worked up by adding water (5 ml) and ice. The aqueous phase was neutralized by addition of saturated NaHCO3 solution, and saturated with NaCl. The aqueous phase was extracted into dichloromethane (3×60 ml), then the organic extracts combined and washed with brine (10 ml) and dried (NaSO4). The product was purified by chromatography on silica (18 g; eluent 2.5%, 5%, then 15% ethyl acetate/hexane). The first compound to elute was unreacted 3-ethoxy-6-methoxy-1,2-benzisoxazole, (46 mg), followed by 3-ethoxy-6-hydroxy-1,2-benzisoxazole 108 mg (65%).
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