Pertrifluoroacetic acid is prepared in situ by the addition of 30% H2O2 solution (0.15 mL) to trifluoroacetic anhydride (0.45 mL) in 5 mL of methylene chloride at 0° C. This solution is stirred at 0° C. for ten minutes, at 25° C. for 30 minutes and then cooled back to 0° C. (S)-N-[[3-[3-fluoro-4-[4-(methylsulfonyl)-1-piperazinyl]phenyl]-2-oxo-5-oxazolidinyl]-methyl]acetamide (VIII-G, R1=COCH3, R9=CH3, X1=F, X2=H) (0.207 g) is added and the reaction is stirred at 25° C. for 30 minutes and then concentrated. The residue is chromatographed on silica gel using 10% methanol (saturated with ammonia) in chloroform as the eluent to afford 0.14 g the N-oxide as a hydrate.
