Br[C:2]1[C:15]([CH3:16])=[CH:14][C:5]([O:6][Si:7]([C:10]([CH3:13])([CH3:12])[CH3:11])([CH3:9])[CH3:8])=[CH:4][C:3]=1[CH3:17].C[Li].[Li+].[Br-].[Li]C(CC)C.CN([CH:30]=[O:31])C>C1COCC1.CCOCC.C1CCCCC1>[C:10]([Si:7]([CH3:9])([CH3:8])[O:6][C:5]1[CH:14]=[C:15]([CH3:16])[C:2]([CH:30]=[O:31])=[C:3]([CH3:17])[CH:4]=1)([CH3:13])([CH3:12])[CH3:11]
To a solution of (4-bromo-3,5-dimethylphenoxy)-tert-butyl-dimethylsilane (3.1 g, 9.8 mmol) in THF (30 mL) at −78° C. under N2 protection was added dropwise methyllithium/LiBr (9.3 ml of a 1.5 M solution in Et2O, 14 mmol). After 5 min of stirring, sec-BuLi (10 mL of a 1.4 M solution in cyclohexane, 14 mmol) was added slowly to the reaction solution at −78° C. After 5 min, anhydrous DMF (1.5 mL, 20 mmol) was added slowly then the solution was warmed to 25° C. After 30 min, the reaction mixture was quenched with water. The aqueous layer was extracted with CH2Cl2 and the combined organic layers were washed with water, brine, dried with MgSO4 and filtered. The solvent was removed under reduced pressure and the residue was purified by flash chromatography using heptane/EtOAc (6:1) to give 4-(tert-butyldimethyl-silanyloxy)-2,6-dimethylbenzaldehyde as a yellow oil.
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