[Cl:1][C:2]1[CH:7]=[C:6]([F:8])[C:5]([Si:9]([CH3:12])([CH3:11])[CH3:10])=[C:4]([F:13])[CH:3]=1.CC1CCCN(C)C1(C)C.[Li].CN([CH:28]=[O:29])C>C1COCC1>[Cl:1][C:2]1[C:3]([CH:28]=[O:29])=[C:4]([F:13])[C:5]([Si:9]([CH3:10])([CH3:12])[CH3:11])=[C:6]([F:8])[CH:7]=1A solution of 1-chloro-3,5-difluoro-4-trimethylsilylbenzene (1.5 g, 6.8 mmol) in THF (10 mL) was added to a solution of lithium tetramethylpiperidine (14 mmol) in THF (15 mL) at −75° C. The solution was stirred for 2 hours then DMF (1.5 g, 20 mmol) was added and the solution allowed to warm to ambient temperature. The reaction was quenched with a saturated solution of ammonium chloride (25 mL) and extracted with ethyl ether (2×25 mL) and the combined extracts dried (sodium sulfate) and concentrated. The residue was purified by chromatography (hexanes) to give 6-chloro-2,4-difluoro-3-trimethylsilylbenzaldehyde (1.4 g, 5.6 mmol): LC/MS (m/z=248).
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