Hydrochloric Acid → 5-Phenoxy-1,3-dihydro-2,1-benzoxaborol-1-ol

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A solution of n-butyl lithium in n-hexanes (2.24 M, 8.6 mL, 0.019 mol) was slowly added to a solution of (2-bromo-5-phenoxyphenyl)methanol (2.21 g, 0.0079 mol) in anhydrous tetrahydrofuran (50 mL) at −78° C. under an atmosphere of nitrogen. The reaction was stirred for thirty minutes at −78° C., then stirred for twenty minutes at −25° C. The reaction was cooled to −50° C. and triisopropylborate (4.075 g, 0.0216 mol) was slowly added. The reaction was warmed to room temperature and was stirred for one hour. An 1 N aqueous solution of hydrochloric acid (20 mL) was added to achieve pH 5, then the reaction was stirred at room temperature for one hour. The reaction mixture was extracted with ethyl ether (3×40 mL). The combined organic extracts were washed with water (60 mL) and brine (60 mL) and dried over sodium sulfate. The solvents were evaporated under the reduced pressure to give a residue, and the residue was purified by flash column chromatography on silica using ethyl acetate/n-heptane (1:5) followed by ethyl acetate/n-heptane (1:4) as mobile phase to yield 5-phenoxy-1,3-dihydro-2,1-benzoxaborol-1-ol (1.3 g, 0.0058 mol).

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