[F:1][C:2]1[CH:3]=[C:4]([CH:7]=[C:8]([F:10])[CH:9]=1)[C:5]#[N:6].C([N-]C(C)C)(C)C.[Li+].CN(C)[CH:21]=[O:22].C(O)(=O)C>O1CCCC1.O>[F:1][C:2]1[CH:3]=[C:4]([CH:7]=[C:8]([F:10])[C:9]=1[CH:21]=[O:22])[C:5]#[N:6]To a solution of 3,5-difluorobenzonitrile (1 gm, 7.1 mmol) in dry tetrahydrofuran (20 mL), lithium diisopropylamide (0.769 gm, 7.1 mmol) was added at −78° C. The resulting reaction mixture was stirred for about 1 hour. Dimethylformamide (0.62 g, 8.5 mmol) was added dropwise to the reaction mixture and stirring was continued for about 45 minutes. Acetic acid (1.5 mL) and water (40 mL) were added to the cold solution of reaction mixture. The aquoeus phase was extracted with diethyl ether (4×50 mL). The combined organic layer was dried over anhydrous sodium sulfate, filtered and concentrated. The crude product was purified by silica gel (100-200) column chromatography using hexane and ethyl acetate as gradient system to afford pure 3,5-difluoro-4-formylbenzonitrile (0.5 gm, 31.25%).
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