The general procedure for the synthesis of tert-butyl D-pyroglutamate from tert-butyl acetate and D-(+)-pyroglutamic acid was as follows: (R)-5-oxopyrrolidine-2-carboxylic acid (3.21 g, 24.9 mmol) was dissolved in tert-butyl acetate (100 mL) under argon protection. Subsequently, 60% aqueous perchloric acid (1.5 mL) was slowly added at room temperature. The reaction mixture was stirred at room temperature for 24 hours in an argon atmosphere. Upon completion of the reaction, saturated aqueous sodium bicarbonate solution (50 mL) was added to the mixture to neutralize the reaction solution, followed by extraction with chloroform (3 x 30 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and the solvent was removed by distillation under reduced pressure to afford tert-butyl (R)-5-oxopyrrolidine-2-carboxylate (4.62 g, yield) as a white solid. The physical properties of the product are described below.
