Trifluoroacetic acid → 1-(Piperidin-4-yl)azetidin-2-one

To a solution of 4-(2-methoxycarbonyl-ethylamino)-piperidine-1-carboxylic acid tert-butyl ester (3.4 g, 12.0 mmol) in anhydrous THF (75 mL) was slowly added a solution of methyl magnesium bromide in diethyl ether (3 M, 6 mL, 18 mmol) at 0° C. The reaction mixture was stirred at 0° C. for 3 h, then allowed to warm to RT and stirring was continued for 72 h. The reaction mixture was concentrated in vacuo and the resulting residue was partitioned between EtOAc and an aqueous solution of ammonium chloride. The organic layer was separated and washed with brine, then dried (Na2SO4) and concentrated in vacuo. The resultant residue was purified by column chromatography to give 4-(2-oxo-azetidin-1-yl)-piperidine-1-carboxylic acid tert-butyl ester as a pale yellow oil (598 mg, 20%). To a solution of 4-(2-oxo-azetidin-1-yl)-piperidine-1-carboxylic acid tert-butyl ester (595 mg, 2.34 mmol) in DCM (6 mL) was added TFA (2 mL). The resulting mixture was stirred at RT for 1.5 h, then concentrated in vacuo. The resultant residue was loaded onto an Isolute® SCX-2 cartridge, washed with MeOH then eluted with 2 M NH3 in MeOH to give the title compound as a pale yellow solid (325 mg, 90%).