At -78 °C, methylhydrazine (5 g, 108.7 mmol) was dissolved in 15-20 mL of dichloromethane containing triethylamine (13.2 g, 130.4 mmol). Benzyl chloroformate (14.8 g, 86.9 mmol) at the same temperature was slowly added dropwise, and the reaction mixture was stirred at this temperature for 15 min before being brought to room temperature and continued to stir under nitrogen protection for 4 hr until thin-layer chromatography (TLC) analysis showed complete consumption of the feedstock. Upon completion of the reaction, the reaction was quenched by the addition of water and the product was extracted with ethyl acetate. The organic phases were combined, washed sequentially with water (50 mL x 2) and saturated saline (50 mL), and dried over anhydrous sodium sulfate. The solvent was concentrated under reduced pressure and the resulting crude product was purified by column chromatography (eluent: hexane solution of 25% ethyl acetate) to afford 8 g of the target product 1-Cbz-1-methylhydrazine (compound 20b). Liquid chromatography-mass spectrometry (LCMS) analysis result: 180.09 (M + H)+.
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