Tetramethylguanidine azide (TMGA) (5.398 g, 37.70 mmol) was added dropwise (5 min) to a 25° C. solution of (4R)-4-benzyl-3-[(2R)-2-bromo-3-butylheptanoyl]-1,3-oxazolidin-2-one (4.0 g, 9.42 mmol) in acetonitrile (50 mL). The reaction was stirred for 4 days. An aliquot was taken and TLC (1:4 EtOAc-hexane) indicated that reaction was complete. The solvent was removed in vacuo. The resulting black semi-solid was dissolved in CH2Cl2 (200 mL) and quenched with 1N HCl (30 mL). The organic layer was dried over MgSO4, filtered, and concentrated in vacuo to obtain (4R)-3-[(2S)-2-azido-3-butylheptanoyl]-4-benzyl-1,3-oxazolidin-2-one as a crude yellow oil (3.61 g, 99.1%). Mass Spectrum (−ESI): 385 (M−H)−.
