NOVELTY - Preparation of N-(((5S)-3-(3-fluoro-4-(morpholin-4-yl)phenyl)-2-oxo-1,3-oxazolidin-5-yl)methyl)acetamide (linezolid) (I) comprises e.g. (a) reacting pyrrolidine-2,5-dione (II) with ((S)-2-(chloromethyl)oxirane) (III) in presence of phase transfer catalyst in organic solvent and a base to obtain (S)-1-(oxiran-2-ylmethyl)pyrrolidine-2,5-dione (IV), and (b) reacting (IV) with 3-fluoro-4-morpholinoaniline (V) in presence of a polar solvent to give (S)-1-(3-((3-fluoro-4-morpholinophenyl)amino)-2-hydroxypropyl)pyrrolidine-2,5-dione (VI).    USE - The method is useful for preparing N-(((5S)-3-(3-fluoro-4-(morpholin-4-yl)phenyl)-2-oxo-1,3-oxazolidin-5-yl)methyl)acetamide (claimed), which is useful for treating serious infections caused by gram-positive bacteria including multi-resistant bacteria of streptococcus and methicillin-resistant Staphylococcus aureus. No biological data given.    ADVANTAGE - The method: is simple, environmental friendly and cost-effective; can be prepared from easily available raw materials which do not require special storage conditions or any special equipments like autoclave; and provides linezolid with good yield and without impurities.    DETAILED DESCRIPTION - Preparation of N-(((5S)-3-(3-fluoro-4-(morpholin-4-yl)phenyl)-2-oxo-1,3-oxazolidin-5-yl)methyl)acetamide (linezolid) of formula (I) comprises: either (a) reacting pyrrolidine-2,5-dione of formula (II) with ((S)-2-(chloromethyl)oxirane) of formula (III) in presence of phase transfer catalyst in organic solvent and a base to obtain (S)-1-(oxiran-2-ylmethyl)pyrrolidine-2,5-dione of formula (IV), (b) reacting (IV) with 3-fluoro-4-morpholinoaniline of formula (V) in presence of a polar solvent to give (S)-1-(3-((3-fluoro-4-morpholinophenyl)amino)-2-hydroxypropyl)pyrrolidine-2,5-dione of formula (VI), (c) reacting (VI) with carbonyl diimidazole in presence of polar organic solvent to obtain (S)-1-((3-(3-fluoro-4-morpholinophenyl)-2-oxooxazolidin-5-yl)methyl)pyrrolidine-2,5-dione of formula (VII), and (d) reacting (VII) in organic solvent with hydrazine hydrate or methylamine to provide (5S)-5-(aminomethyl)-3-(3-fluoro-4-(morpholin-4-yl)phenyl)-1,3-oxazolidin-2-one of formula (IX), which is not isolated and in-situ treated with acetic anhydride in presence of organic solvent to obtain (I); or reacting methyl (3-fluoro-4-morpholinophenyl)carbamate of formula (VIII) with alkyl alkali metal compound in inert solvent or alkali alkoxide in presence of polar solvent and (S)-1-(oxiran-2-ylmethyl)pyrrolidine-2,5-dione (IV).