General procedure for the synthesis of 1-tert-butyl-4-oxopyrrolidine-2-carboxylic acid from 1-(tert-butoxycarbonyl)-4-hydroxypyrrolidine-2-carboxylic acid: 1-(tert-butoxycarbonyl)-4-hydroxypyrrolidine-2-carboxylic acid (178 g, 0.77 mol) was dissolved in dichloromethane (2.0 L), trichloroisocyanuric acid (178.89 g, 0.77 mol), followed by 2,2,6,6-tetramethylpiperidine oxide (6.05 g, 0.0385 mol). The reaction mixture was stirred at room temperature for 1 hour. After completion of the reaction, the reaction was quenched with water and the insoluble material was removed by filtration. The aqueous phase was extracted several times with dichloromethane, all organic phases were combined and dried with anhydrous sodium sulfate. Finally, the organic phase was concentrated to dryness under vacuum to give 1-tert-butyl-4-oxopyrrolidine-2-carboxylic acid (180 g) in 100% yield.
