[C:1]([Si:5]([O:8][C:9]1[CH:14]=[C:13]([F:15])[C:12]([F:16])=[CH:11][C:10]=1[O:17][CH3:18])([CH3:7])[CH3:6])([CH3:4])([CH3:3])[CH3:2].C([Li])CCC.CN(C)[CH:26]=[O:27].[Cl-].[NH4+]>O1CCCC1.O>[C:1]([Si:5]([CH3:7])([CH3:6])[O:8][C:9]1[C:10]([O:17][CH3:18])=[C:11]([C:12]([F:16])=[C:13]([F:15])[CH:14]=1)[CH:26]=[O:27])([CH3:4])([CH3:3])[CH3:2]To a solution of tert-butyl-(4,5-difluoro-2-methoxy-phenoxy)-dimethyl-silane (5.2 g, 18.95 mmol) in tetrahydrofuran (60 mL) cooled to −78° C. was added n-butyllithium (9.096 mL, 22.74 mmol) dropwise over a period of 15 minutes. At the end of the addition, the reaction mixture was stirred at −78° C. for 1 hour. Dimethylformamide (1.737 mL, 22.74 mmol) was added and the reaction mixture was stirred at −78° C. for 2 hours. Saturated solution of ammonium chloride (˜5 mL) was added, and then the mixture was diluted with 100 mL of water. The aqueous layer was extracted with ethyl acetate (2×75 mL). The combined organic layers were washed with brine and dried over anhydrous magnesium sulfate. The solids were filtered off and the filtrate was concentrated in vacuo. Purification of the crude residue by flash chromatography (Biotage system, 60 Å silica gel, eluting with 4% ethyl acetate in hexanes) yielded 3-(tert-butyl-dimethyl-silanyloxy)-5,6-difluoro-2-methoxy-benzaldehyde as clear oil (3.96 g, 69%). LR-MS (M+) 302.2.
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