(S)-6-{[(Benzyl-oxy)carbonyl]amino}-2-bromohexanoic acid, 10.0 g (0.029 mole), was dissolved in chloroform, 20 mL. To this was added a solution of t-butyl trichloroacetimidate, 12.7 g (0.058 mole), dissolved in chloroform, 50 mL, drop-wise over 30 minutes. The mixture was allowed to stir an additional 5 minutes and boron trifluoride etherate, 100 μL, was added. The reaction mixture was allowed to stir overnight. Sodium bicarbonate, 5 g, was added. After stirring 10 minutes, hexanes, 50 mL, was added and the mixture filtered to remove the solids present. The filtrate was evaporated and the residue purified by flash chromatography, ethyl acetate-hexanes, to give a clear-colorless oil. The yield was 8.5 g, 73% based on starting (S)-6-{[(benzyloxy)carbonyl]amino}-2-bromohexanoic acid. NMR is consistent with structure.
