Synthesis
General procedure for the synthesis of 4-morpholinopiperidine trifluoroacetate from 2,2,2-trifluoroacetic acid and 4-(4-piperidinyl)morpholine: To a stirred solution of tert-butyl 4-oxo-piperidine-1-carboxylate (3.0 g, 15 mmol) in THF (25 mL) were sequentially added morpholine (1.56 g, 18 mmol) and tetraisopropyl titanate (5.58 mL). The reaction mixture was stirred at room temperature for 1 hour. Subsequently, ethanol (15 mL) was added followed by sodium cyanoborohydride (0.63 g, 10.05 mmol). The resulting mixture was stirred at room temperature overnight and the reaction was quenched by the addition of water (4 mL). After continued stirring for 30 min, the white solid was removed by filtration and the filtrate was concentrated by evaporation. The residue was partitioned between ether and water, and the organic layer was separated and dried over anhydrous sodium sulfate. The solvent was removed under reduced pressure to give a white solid. The solid was dissolved in 40 mL of 50% trifluoroacetic acid in dichloromethane solution and stirred at room temperature for 1 hour before removing the solvent. The residue was lyophilized to give the target product 4-morpholinopiperidine trifluoroacetate as a white solid (5.48 g, 98% yield). Mass spectrometry analysis showed that the (M+H)+ peak was located at m/z 171.
