[CH3:1][C:2]1[CH:7]=[CH:6][C:5]([S:8]([N:11]2[CH2:16][CH2:15][CH:14]([C:17]3[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=3)[CH2:13][CH2:12]2)(=[O:10])=[O:9])=[CH:4][CH:3]=1.ClC[CH:25]([O:28]C(CCl)CCl)CCl>ClCCl.[Ti](Cl)(Cl)(Cl)Cl>[CH3:1][C:2]1[CH:3]=[CH:4][C:5]([S:8]([N:11]2[CH2:16][CH2:15][CH:14]([C:17]3[CH:22]=[CH:21][C:20]([CH:25]=[O:28])=[CH:19][CH:18]=3)[CH2:13][CH2:12]2)(=[O:9])=[O:10])=[CH:6][CH:7]=1To a solution of 1-(4-methylphenylsulfonyl)-4-phenylpiperidine (1.0 g) and 1,1-dichloromethylmethylether (0.57 ml) in dichloromethane (5 ml) was added at 0° C. a solution of titanium tetrachloride (0.7 ml) in dichloromethane (5 ml), and the mixture was stirred at room temperature for 2 hours. The mixture was added to stirred ice/water to stop the reaction. The mixture was extracted with ethyl acetate. The organic layer was washed with sodium bicarbonate solution and saturated brine and dried with magnesium sulfate. Under reduced pressure, the mixture was concentrated, and the residue was purified with column chromatography (ethyl acetate/hexane=1:4→1:2) to give pale yellow crystals of 4-[1-(4-methylphenylsulfonyl)piperidin-4-yl]benzaldehyde (0.381 g). (469.4 mg of the starting materials were collected)
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