Hydrochloric Acid → 5-Fluoro-2-piperidin-1-yl-phenylamine

Concentrated hydrochloric acid (1.20 ml, 14.4 mmol) and anhydrous tin dichloride (1.22 g, 6.43 mmol) were sequentially added at 0° C. to a methanol (5 ml) solution of 1-(4-fluoro-2-nitrophenyl)piperidine (289 mg, 1.28 mmol), obtained as described in Referential Example 17-1. The resulting mixture was warmed to room temperature and stirred for 21 hours. A saturated aqueous solution of sodium bicarbonate was added to the mixture. The mixture was extracted three times with ethyl acetate. The obtained organic layer was washed with a saturated sodium chloride solution, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (25 g, hexane/ethyl acetate=12/1). Thus, 5-fluoro-2-(1-piperidinyl)aniline (250 mg, quant.) was yielded as a colorless oily material.