in 200 ml of methanol monoperoxyphthalic acid magnesium salt hexahydrate 80 pure 11 5 g is added and the resulting suspension is stirred at 25 u00b0 c for two hours the reaction mixture is filtered and the filtrate is concentrated to afford a light yellow solid this material is chromatographed on silica gel using 10 methanol saturated with ammonia in chloroform as eluent to afford 8 75 g of the n oxide ir mull 1747 1669 1620 1556 1508 1495 1445 1413 1341 1295 1269 1232 1204 1124 755cm u2212 1 ms fab m z 354 708 707 355 354 339 338 337 336 86 56 pertrifluoroacetic acid is prepared in situ by the addition of 30 h 2 o 2 solution 0 15 ml to trifluoroacetic anhydride 0 45 ml in 5 ml of methylene chloride at 0 u00b0 c this solution is stirred at 0 u00b0 c for ten minutes at 25 u00b0 c for 30 minutes and then cooled back to 0 u00b0 c s n 3 3 fluoro 4 4 methylsulfonyl 1 piperazinyl phenyl 2 oxo 5 oxazolidinyl methyl acetamide vii g r 1 u2550 coch 3 r 9 u2550 ch 3 x 1 u2550 f x 2 u2550 h 0 207 g is added and the reaction is stirred at 25 u00b0 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 of the n oxide as a hydrate ir mull 1751 1668 1658 1503 1443 1408 1340 1328 1277 1260 1226 1157.