Methyl 2-(4-(trifluoromethyl)phenyl)piperidine-4-carboxylate (4.973 g, 17.31 mmol) was dissolved in DCM (100 mL) and DIPEA (3.62 mL, 20.77 mmol) added followed by methyl carbonochloridate (1.636 mL, 20.77 mmol). The solution was stirred at room temperature for 1 h 45 min. The reaction mixture was washed with 0.1 M HCl and satd NaHCO3. The organic phase was passed through a phase separator and evaporated to yield crude dimethyl 2-(4-(trifluoromethyl)phenyl)piperidine-1,4-dicarboxylate (6.05 g, 101%) as a brown oil. MS m/z 346 (M+H)+
