11-1) Preparation of benzyl (2S,3S)-(1-amino-3-methyl-1-oxopentan-2-yl)carbamate
2.63 g (10 mmol) of (2S,3S)-2-(((benzyloxy)carbonyl)amino)-3-methylpentanoic acid was added to a 100 mL solution of dichloromethane pre-cooled to -20°C. 1.40 mL of triethylamine and 1.23 mL of tertiary chloroyl chloride were added sequentially. after 30 min, an ammonia gas bulge was passed into the reaction mixture for 30 min. The resulting precipitate was filtered and the solid was washed with 50 mL of methylene chloride. The combined organic phases were washed sequentially with 2N HCl solution (50 mL x 2) and 50 mL saturated brine. The organic layer was dried with anhydrous MgSO4 and concentrated in vacuum to give 2.49 g (2S,3S)-(1-amino-3-methyl-1-oxopentan-2-yl)carbamic acid benzyl ester (yield: 95%).
1H NMR (CDCl3) δ: 0.9 (m, 6H), 1.2 (m, 1H), 1.5 (m, 1H), 1.8 (m, 1H), 4.0 (m, 1H), 5.1 (s, 2H), 6.5 (d, 1H).
