In dichloromethane (100 ml) was dissolved t-butyl 4-[(4-chlorophenyl)sulfonyl]-4-(2,5-difluorophenyl)-1-piperidinecarboxylate (3.17 g, 6.72 mmol), followed by the dropwise addition of trifluoroacetic acid (10.0 ml) under ice cooling. After stirring at room temperature for 2 hours, the reaction mixture was concentrated under reduced pressure. To the residue thus obtained was added a 1N solution (30 ml) of hydrochloric acid in ethanol. The resulting mixture was concentrated under reduced pressure to give a white solid. The white solid thus obtained was washed with diethyl ether, whereby the title compound (2.74 g, 6.71 mmol, quant.) was obtained as a white powder.
