Hydrochloric Acid → 4-Bromo-6,7-difluoro-2-methylbenzofuran-5-ol

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Reaction Steps

107.1 ml (0.17 mol) of n-BuLi (15% soln. in hexane) are initially introduced at −70° C. in 150 ml of THF, and 29.0 ml (0.17 mol) of 2,2,6,6-tetramethylpiperidine are added. After 30 min at this temperature, a solution of 38.3 g (0.16 mol) of 4-bromo-6,7-difluoro-2-methylbenzofuran in 100 ml of THF is metered in. After 3 h at this temperature, 19.1 ml (0.17 mol) of trimethyl borate are added dropwise, and the batch is warmed to room temperature. 40 ml of dilute acetic acid (about 30%) are added, and 40 ml of aqueous hydrogen peroxide soln. (35%) are carefully added to the batch. When the addition is complete, the mixture is stirred at 20° C. for 18 h. Water is added, and the batch is acidified using HCl. The solution is extracted a number of times with MTBE, and the combined organic phases are washed successively with water, sat. sodium chloride soln. and ammonium iron(II) sulfate soln. The solution is dried using sodium sulfate and concentrated to dryness. The crude product is purified by column chromatography (SiO2, n-heptane:1-chlorobutane=2:1), giving 4-bromo-6,7-difluoro-2-methylbenzofuran-5-ol as a beige solid.

Provenance & Evidence