Hydrochloric Acid → 6-(2,6-Dimethoxyphenyl)-1-(4-(trifluoromethoxy)benzyl)piperazine-2,5-dione

A cooled (0° C.) solution of ethyl 2-(2-((tert-butoxycarbonyl)amino)-N-(4-(trifluoromethoxy)-benzyl)acetamido)-2-(2,6-dimethoxyphenyl)acetate (900 mg; 1.57 mmol) in anh. DCM (18 ml) was treated dropwise with 4 M HCl in dioxane (6.00 ml; 24.00 mmol), and the resulting mixture was further stirred at rt, under nitrogen, for 2.5 h. The reaction mixture was concentrated to dryness under reduced pressure, the resulting residue was treated with aq. sat. NaHCO3 (7.5 ml) and AcOEt (7.5 ml), and stirring at rt was then continued for 17 h. The separated aq. layer was extracted with AcOEt (20 ml), and the mixed organic layers were washed with brine, dried over anh. MgSO4, filtered, and concentrated to dryness under reduced pressure affording 6-(2,6-dimethoxyphenyl)-1-(4-(trifluoromethoxy)benzyl)-piperazine-2,5-dione as a slightly orange solid. LC-MS (conditions D): tR=0.94 min.; [M+H]+: 424.88 g/mol.