[O:1]1[C:5]([CH2:6][C:7]#[N:8])=[CH:4][CH:3]=[N:2]1.O=[C:10]1[CH2:15][CH2:14][N:13]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:12][CH2:11]1.C([O-])(=O)C.[NH4+]>C1(C)C=CC=CC=1>[C:7]([C:6]([C:5]1[O:1][N:2]=[CH:3][CH:4]=1)=[C:10]1[CH2:15][CH2:14][N:13]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:12][CH2:11]1)#[N:8]A mixture of isoxazol-5-ylacetonitrile from Example 48A (3.00 g, 27.8 mmol), tert-butyl 4-oxopiperidine-1-carboxylate (5.53 g, 27.8 mmol) and ammonium acetate (4.28 g, 55.5 mmol) in toluene (50 mL) was heated for 8 h to reflux. Subsequently, the mixture was extracted with water, dried over sodium sulfate, and the solvent was removed in vacuo. The crude product was purified by column chromatography on silica gel (eluent: cyclohexane/ethyl acetate 2:1) to yield an oil, which precipitated upon treatment with petroleum ether/tert-butyl methyl ether to yield 4.38 g (54.6%) of the title compound as yellowish crystals.
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