1. In a 100 mL oven-dried round-bottomed flask, N-tert-butoxycarbonyl-L-alanine (3.0 g, 15.8 mmol), anhydrous dichloromethane (60 mL), and N,N-diisopropylethylamine (2.5 mL, 14.2 mmol) were added, and the mixture was cooled to 0 °C.
2. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (3.7 g, 19.0 mmol) and 1-hydroxybenzotriazole (2.6 g, 19.0 mmol) were added sequentially at 0 °C and stirred for 10 min.
3. N,O-dimethylhydroxylamine hydrochloride (1.9 g, 19.0 mmol) and N,N-diisopropylethylamine (3.3 mL, 19.0 mmol) were added, and stirring was continued for 1 hr at 0 °C, then the reaction was raised to 25 °C for 16 hr.
4. After completion of the reaction, the reaction mixture was diluted with dichloromethane (300 mL) and the organic layer was washed sequentially with 2N hydrochloric acid (3 x 180 mL), saturated sodium bicarbonate solution (2 x 180 mL) and brine (2 x 180 mL).
5. The organic phase was dried with anhydrous sodium sulfate and concentrated under reduced pressure to give a white solid product (3.6 g, 99% yield).
6. The above product (3.7 g, 15.8 mmol) was dissolved in anhydrous tetrahydrofuran (100 mL) and cooled to 0°C. The product was added to the mixture.
7. Lithium aluminum hydride (660 mg, 17.4 mmol) was added and stirred for 20 min.
8. Upon completion of the reaction, the organic layer was quenched with 5% hydrochloric acid solution, evaporated and the aqueous phase was extracted with ethyl acetate (3 x 30 mL).
9. The organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to give N-(tert-butoxycarbonyl)-L-alanine-N-methoxy-N-methylamide white solid (2.6 g, 94% yield).
