[CH2:1]([CH:8]1[CH:12]([C:13](O)=[O:14])[O:11][C:10](=[O:16])[NH:9]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.S(=O)(=O)(O)O.C[O-].[Na+].[BH4-].[Na+].Cl>CO.O>[CH2:1]([C@H:8]1[C@@H:12]([CH2:13][OH:14])[O:11][C:10](=[O:16])[NH:9]1)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1
A solution of 50 g of a 97.2:2.8 mixture of the (4S,5S):(4S,5R) isomers of 4-benzyl-2-oxo-oxazolidine-5-carboxylic acid in 300 ml of methanol was combined with 1 ml of sulphuric acid and refluxed for 3.5 hours. The solution was cooled to 0° C. and adjusted to pH 7 with a solution of 30% sodium methoxide in methanol. 10.26 g of sodium borohydride were added to the solution at 0-3° C. After 1 hour's stirring at 0° C., the suspension is adjusted to pH 1 at 0-20° C. with 25% hydrochloric acid. After the addition of water and stirring at -10° C., the suspension is filtered. 41.5 g (89%) of 99% (4S,5S)-4-benzyl-5-hydroxymethyl-oxazolidin-2-one, melting point 168-171° C., [α]D20 : -79.1° (1% in methanol), were obtained.
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