(R)-2-Amino-2-methylbutyric acid (2.05 g, 17.50 mmol), triethylamine (7.01 mL, 50.20 mmol) and di-tert-butyl dicarbonate (5.70 g, 26.00 mmol) were sequentially added to the reaction flask under nitrogen protection. Subsequently, tetrahydrofuran (20 mL) was added as a solvent and the reaction mixture was heated to the appropriate temperature for the reaction. After completion of the reaction, the mixture was cooled to room temperature. Extraction was carried out with ethyl acetate (50 mL x 3), the organic phases were combined and dried with anhydrous Na2SO4. The solvent was removed by distillation under reduced pressure to give the crude product. Purification by column chromatography (eluent: dichloromethane/methanol (v/v)=10/1) afforded 3.60 g of the colorless oily target product (R)-2-((tert-butoxycarbonyl)amino)-2-methylbutyric acid in 97.0% yield.
