C([Si](C)(C)[O:6][C:7]1[C:8]([F:23])=[C:9]([CH:12]=[C:13](O[Si](C(C)(C)C)(C)C)[CH:14]=1)[CH:10]=[O:11])(C)(C)C.[F-].[K+].[CH3:28]I.CN([CH:33]=[O:34])C>O>[F:23][C:8]1[C:7]([O:6][CH3:28])=[CH:14][C:13]([O:34][CH3:33])=[CH:12][C:9]=1[CH:10]=[O:11]A mixture of the 3,5-bis-(tert-butyl-dimethyl-silanyloxy)-2-fluoro-benzaldehyde (3.0 g, 7.8 mmol) obtained in Example 251.1, potassium fluoride (1.81 g, 31.2 mmol), methyl iodide (1.17 ml, 18.7 mmol) and DMF (25 ml) was stirred for 2 h. at room temperature. Water (25 ml) was added and the mixture was extracted with diethyl ether. The organic phase was washed with water, dried, filtered and concentrated. The residue was purified by chromatography (SiO2, cyclohexane/EtOAc 18:11:1). There was obtained 0.87 g (60%) of 2-fluoro-3,5-dimethoxy-benzaldehyde as a colorless solid.
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