To a solution of 4-fluoro-2-(trifluoromethyl)benzonitrile (5 g, 26 mmol,) in DMSO (50 ml) was added tert-butyl 4-aminopiperidine-1-carboxylate (5.3 g, 26.5 mmol, 1 eq.) and potassium carbonate (7.3 g, 52.8 mmol, 2 eq.). The resulting solution was stirred with heating overnight at 100° C. (oil bath). The resulting solution was diluted with of ethyl acetate (300 ml) and washed with sodium chloride (sat., 300 ml). The organic layer was dried over anhydrous sodium sulfate, filtered, and concentrated under vacuum to give a residue, which was applied onto a silica gel column and eluted with ethyl acetate to afford tert-butyl 4-[[4-cyano-3-(trifluoromethyl)phenyl]amino]piperidine-1-carboxylate as a white powder (5 g, 51%). (ES, m/z):[M+H]+ 370.1.
