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0 °C

Ethyl 2-(3,5-dibromothiophen-2-yl)-2-hydroxyacetate (7b) (100 mg, 0.29 mmol) was dissolved in tert-butyl acetate (5.4 mL) at −20° C. and 70% perchloric acid (0.7 mL) was rapidly added. The mixture was stirred at 0° C. for 3 hours then poured in a saturated solution of potassium carbonate. Layers were separated. The aqueous layer was extracted with ethyl acetate (2×20 mL). The organic layers were washed with brine (10 mL), dried over sodium sulfate and concentrated in vacuo. The residue was purified by flash chromatography on silica gel (cyclohexane/ethyl acetate 90/10) to provide ethyl 2-(tert-butoxy)-2-(3,5-dibromothiophen-2-yl)acetate (100 mg, 0.40 mmol, 86%).

1. customLayers were separated
2. extractionThe aqueous layer was extracted with ethyl acetate (2×20 mL)
3. washThe organic layers were washed with brine (10 mL)
4. dry with materialdried over sodium sulfate
5. concentrationconcentrated in vacuo
6. customThe residue was purified by flash chromatography on silica gel (cyclohexane/ethyl acetate 90/10)