[CH3:1][CH:2]([C:4]1[N:8]=[C:7]([N:9]2[CH2:14][CH2:13][CH:12]([CH2:15][OH:16])[CH2:11][CH2:10]2)[O:6][N:5]=1)[CH3:3].[Cr](Cl)([O-])(=O)=O.[NH+]1C=CC=CC=1.CCOCC>C(Cl)Cl>[CH3:3][CH:2]([C:4]1[N:8]=[C:7]([N:9]2[CH2:14][CH2:13][CH:12]([CH:15]=[O:16])[CH2:11][CH2:10]2)[O:6][N:5]=1)[CH3:1]A solution of {1-[3-(1-methylethyl)-1,2,4-oxadiazol-5-yl]-4-piperidinyl}methanol (prepared as in Example 20, Step 3, 1.50 g, 6.33 mmol) in CH2Cl2 (30 mL) was treated with pyridinium chlorochromate (2.09 g, 9.49 mmol). The reaction mixture was stirred at ambient temperature for 5 h. Et2O (50 mL) was added, and the mixture was stirred for 10 min, filtered through a plug of Celite® on top of a layer of silica gel and the filtrate was concentrated. The resulting brown residue was mixed with Et2O (100 mL) and filtered. The filtrate was dried over Na2SO4, filtered and concentrated to give 1.10 g (78%) of 1-[3-(1-methylethyl)-1,2,4-oxadiazol-5-yl]-4-piperidinecarbaldehyde as a light brown oil which was used without further purification. 1H NMR (400 MHz, CDCl3): δ 9.69 (s, 1H), 4.15-4.00 (m, 2H), 3.30-3.20 (m, 2H), 2.88 (septet, 1H, J=7.0 Hz), 2.55-2.45 (m, 1H), 2.10-1.95 (m, 2H), 1.80-1.65 (m, 2H), 1.27 (d, 6H, J=6.9 Hz).
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