[Br:1][CH2:2][CH2:3][CH:4]([CH3:8])[C:5]([OH:7])=[O:6].[CH3:9]O>OS(O)(=O)=O>[CH3:9][O:6][C:5](=[O:7])[CH:4]([CH3:8])[CH2:3][CH2:2][Br:1]4-Bromo-2-methyl-butyric acid (2.16 g, 1 eq, prepared according to the procedure described in J. Am. Chem. Soc. 1990, 112, 2755) was dissolved in MeOH (10 mL) and a few drops of conc. H2SO4 were added. The reaction was stirred at reflux for 16 hours. After reaction completion, as monitored by LC-MS, MeOH was removed under reduced pressure, the oily residue was diluted with water, the pH adjusted to 9 with 10% NaOH, and the product was extracted with Et2O (2×20 mL) and dried over Na2SO4. The title compound was obtained as a colourless oil (1.29 g, 55% yield) after solvent removal.
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