Benzyl chloroformate → Methyl 2-(2-(((benzyloxy)carbonyl)amino)pent-4-ynamido)-4-methylpentanoate

To a solution of compound 2 (8.5 g; 31 mmol) in dry THF (100 mL) was added DIEA (16.02 g; 124 mmol) and the reaction mixture was stirred for 30 min at room temperature. Benzylchloroformate (6.87 g; 40.3 mmol) was added and stirring was continued at room temperature for 16 h. The solvent was removed on the rotary evaporator and the residue was taken up in ethyl acetate (150 mL) and washed sequentially with water (50 mL), 5% HCl (2×50 mL), and brine (50 mL). The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated to give 3 as a white solid (10.46 g: 90% yield). 1H NMR (CDCl3) δ 7.3 (m, 5H), 6.7 (s, 1H), 5.6 (s, 1H), 5.1 (s, 2H), 4.6 (m, 1H), 4.4 (m, 1H), 3.7 (s, 3H), 2.6 (m, 2H), 2.8 (s, 1H), 2.6 (m, 1H), 1.6 (m, 2H), 1.5 (m, 1H), 0.9 (d, 6H).