NaHCO3 (14.5 g, 172 mmol, Eq: 2.5) and H2O (210 mL) were added to a slurry of (R)-2-(benzyloxycarbonylamino)-3-mercapto-3-methylbutanoic acid (19.5 g, 68.8 mmol, Eq: 1.00) in EtOH (70.0 mL). After 20 min. the mixture became homogeneous, 1-fluoro-2-nitrobenzene (9.71 g, 7.00 mL, 68.8 mmol, Eq: 1.00) was added and the mixture heated to reflux for 6 h. The mixture was cooled to RT, poured into H2O (300 mL) and extracted with MTBE. The aqueous layer was acidified to pH 5 with 1 N HCl and extracted with Et2O. The combined organic extracts were dried over Na2SO4 filtered and concentrated to give (R)-2-(benzyloxycarbonylamino)-3-methyl-3-(2-nitrophenylthio)butanoic acid (18.7 g, 67.2%) as a light yellow oil which was used without purification.
