O.[C:2]1(C)C=CC(S(O)(=O)=O)=CC=1.[F:13][C:14]([F:22])([C:18]([OH:21])([CH3:20])[CH3:19])[C:15]([OH:17])=[O:16].C(=O)([O-])O.[Na+]>CO>[F:13][C:14]([F:22])([C:18]([OH:21])([CH3:20])[CH3:19])[C:15]([O:17][CH3:2])=[O:16]A catalytic amount of p-toluenesulfonic acid monohydrate was added to a mixture of 73.3 g of Intermediate 3 in Example 3 and 300 g of methanol. With stirring in a nitrogen atmosphere, the reaction mixture was heated under reflux for 12 hours. After cooling, the reaction mixture was poured into a saturated sodium hydrogen carbonate aqueous solution and extracted with ethyl acetate. The ethyl acetate solution was washed, dried and concentrated. The residue was distilled in vacuum, obtaining 52.0 g (yield 65%) of methyl 2,2-difluoro-3-hydroxy-3-methylbutanoate.
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