N-bromobutanimide → Ethyl 4-(bromomethyl)-2,5-difluorobenzoate

関与物質

反応条件

反応手順

To a solution of ethyl 2,5-difluoro-4-methylbenzoate (Preparation 18, 4.674 g, 23.35 mmol) in 1,2-dichloroethane (70 mL) were added N-bromosuccinimide (4.57 g, 25.68 mmol) and benzoyl peroxide (56 mg, 0.23 mmol) and the mixture was heated to 70° C. for 2 days. The reaction mixture was allowed to cool, quenched with saturated aqueous sodium thiosulfate (20 mL) and diluted with water (50 mL). The organic layer was separated and the aqueous layer extracted with DCM (2×80 mL). The combined organics were washed with saturated aqueous sodium hydrogen carbonate, followed by brine, then filtered through a phase separator and concentrated in vacuo. The resulting yellow oil was redissolved in EtOAc (70 mL), and N,N-diisopropylethylamine (4.04 mL, 23.35 mmol) was added. The mixture was cooled to 0° C., and diethyl phosphate (2.29 mL, 23.35 mmol) was added. After stirring at 0° C. for 90 minutes, LCMS indicated complete conversion of the dibromomethyl impurity to the desired mono-bromomethyl product. The reaction was quenched at 0° C. with water (70 mL), followed by aqueous hydrochloric acid (2N, 10 mL). The organic layer was separated, washed with brine (100 mL), dried over sodium sulfate and concentrated in vacuo to yield a yellow residue. The residue was purified by silica gel chromatography eluting with 0 to 3% EtOAc in heptane to afford the title compound as a clear oil (5.78 g, 89%):

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