(4S,5S)-4-methyl-5-phenyl-1,3-oxazolidin-2-one

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added, at room temperature, to a suspension of 1.89 g of sodium hydride (80% dispersion in vaseline) in 200 cm3 of dry tetrahydrofuran. This suspension is cooled to -30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to -78° C., which is obtained by adding 35.27 cm3 of a 1.6M solution of butyllithium in hexane to a solution, cooled to -78° C., of 10 g of (4S,5S)-4-methyl-5-phenyl-2-oxazolidinone in 200 cm3 of dry tetrahydrofuran, is finally added. The reaction mixture is stirred for 45 minutes at -30° C. and then after reequilibrating to room temperature, 200 cm3 of a saturated aqueous solution of ammonium chloride is added followed by 500 cm3 of ethyl acetate; after decantation, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous solution of sodium chloride, dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 and then 80/20 by volume) and collecting fractions of 50 cm3. Fractions 14 to 31 are pooled and concentrated to dryness under reduced pressure (2.7 kPa). 13.6 g of (4S,5S)-4-methyl5-Phenyl-3-(2-methoxyphenylacetyl)-2-oxazolidinone are obtained in the form of a yellow oil. a solution, cooled to -78° C. which is obtained is finally added after reequilibrating to room temperature after decantation, the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of a saturated aqueous solution of sodium chloride, dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 80/20 by volume) and collecting fractions of 50 cm3 concentrated to dryness under reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added to a suspension of 1.89 [lacuna] of sodium hydride (80% strength dispersion in liquid paraffin) in 200 cm3 of dry tetrahydrofuran at room temperature. This suspension is cooled to -30° C., 7.77 cm3 of pivaloyl chloride are added, and a solution, cooled to -78° C., obtained by adding a solution of 35.27 cm3 of 1.6M butyllithium in hexane to a solution, cooled to -78° C., of 10 g of (4S,5S)-4-methyl-5-phenyloxazolidin-2-one in 200 cm3 of dry tetrahydrofuran, is then finally added. The reaction mixture is stirred at -30° C. for 45 minutes and then, after returning to room temperature, 200 cm3 of an aqueous saturated solution of ammonium chloride and then 500 cm3 of ethyl acetate are added; after separation by settling, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of an aqueous saturated solution of sodium chloride, and is dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) by eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 and then 80/20 by volume) and collecting fractions of 50 cm3. Fractions 14 to 31 are combined and concentrated to dryness under-reduced pressure (2.7 kPa). 13.6 g of (4S,5S)-4-methyl-5-phenyl-3-(2-methoxyphenylacetyl)oxazolidin-2-one are obtained in the form of a yellow oil. a solution, cooled to -78° C. obtained is then finally added after returning to room temperature after separation the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of an aqueous saturated solution of sodium chloride, and is dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) by eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 80/20 by volume) and collecting fractions of 50 cm3 concentrated to dryness under-reduced pressure (2.7 kPa)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a solution of (1S,2S)-(+)-Norpseudoephedrine (2.00 g, 13.2 mmol) in CH2Cl2 (60 mL) was added under argon Et3N (4.61 mL, 33.1 mmol) at 0° C. Then, triphosgene (1.57 g, 5.29 mmol) dissolved in 20 mL of CH2Cl2 was added slowly, and the temperature was allowed to warm from 0° C. to room temperature. The reaction mixture was stirred for 4 hours at room temperature. The reaction mixture was then quenched by addition of aqueous NH4Cl. The organic layers were separated, dried over MgSO4, filtered, and concentrated. The residue was purified by column chromatography using EtOAc in heptane from 0% to 100% in order to give the desired product (2.10 g, 89%). LC-MS: [M+H] 178.1; Rt 0.67 min; (LCMS method 2). 1H NMR (400 MHz, DMSO-d6) 7.88 (br s, 1H), 7.50-7.32 (m, 5H), 5.09 (d, 1H), 3.78-3.62 (m, 1H), 1.26 (d, 3H). was added slowly to warm from 0° C. to room temperature The reaction mixture was then quenched by addition of aqueous NH4Cl The organic layers were separated dried over MgSO4 filtered concentrated The residue was purified by column chromatography

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a solution of (1S,2S)-(+)-Norpseudoephedrine (2.00 g, 13.2 mmol) in CH2Cl2 (60 mL) was added under argon Et3N (4.61 mL, 33.1 mmol) at 0° C. Then, triphosgene (1.57 g, 5.29 mmol) dissolved in 20 mL of CH2Cl2 was added slowly, and the temperature was allowed to warm from 0° C. to room temperature. The reaction mixture was stirred for 4 hours at room temperature. The reaction mixture was then quenched by addition of aqueous NH4Cl. The organic layers were separated, dried over MgSO4, filtered, and concentrated. The residue was purified by column chromatography using EtOAc in heptane from 0% to 100% in order to give the desired product (2.10 g, 89%). LC-MS: [M+H] 178.1; Rt 0.67 min; (LCMS method 2). 1H NMR (400 MHz, DMSO-d6) 7.88 (br s, 1H), 7.50-7.32 (m, 5H), 5.09 (d, 1H), 3.78-3.62 (m, 1H), 1.26 (d, 3H). was added slowly to warm from 0° C. to room temperature The reaction mixture was then quenched by addition of aqueous NH4Cl The organic layers were separated dried over MgSO4 filtered concentrated The residue was purified by column chromatography

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added at room temperature to a suspension of 1.89 g of sodium hydride (80% dispersion in petroleum jelly) in 200 cm3 of dry tetrahydrofuran. This suspension is cooled to −30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to −78° C., obtained by adding a solution of 35.27 cm3 of 1.6M butyllithium in hexane to a solution, cooled to −78° C., of 10 g of (4S,5S)-4-methyl-5-phenyloxazolidin-2-one in 200 cm3 of dry tetrahydrofuran is finally added. The reaction mixture is stirred for 45 minutes at −30° C. and then, after returning to room temperature, 200 cm3 of a saturated aqueous ammonium chloride solution and then 500 cm3 of ethyl acetate are added; after separating by settling, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous sodium chloride solution, dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a column of silica gel (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 and then 80/20 by volume) and collecting 50 cm3 fractions. Fractions 14 to 31 are combined and concentrated to dryness under reduced pressure (2.7 kPa). There are obtained 13.6 g of (4S,5S)-4-methyl-5-phenyl-3-(2-methoxyphenylacetyl)oxazolidin-2-one in the form of a yellow oil. a solution, cooled to −78° C. obtained is finally added after returning to room temperature after separating the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of a saturated aqueous sodium chloride solution, dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a column of silica gel (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 80/20 by volume) and collecting 50 cm3 fractions concentrated to dryness under reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added at room temperature to a suspension of 1.89 g of sodium hydride (80% dispersion in petroleum jelly) in 200 cm3 of dry tetrahydrofuran. This suspension is cooled to −30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to −78° C., obtained by adding a solution of 35.27 cm3 of 1.6M butyllithium in hexane to a solution, cooled to −78° C., of 10 g of (4S,5S)-4-methyl-5-phenyloxazolidin-2-one in 200 cm3 of dry tetrahydrofuran is finally added. The reaction mixture is stirred for 45 minutes at −30° C. and then, after returning to room temperature, 200 cm3 of a saturated aqueous ammonium chloride solution and then 500 cm3 of ethyl acetate are added; after separating by settling, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous sodium chloride solution, dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a column of silica gel (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 and then 80/20 by volume) and collecting 50 cm3 fractions. Fractions 14 to 31 are combined and concentrated to dryness under reduced pressure (2.7 kPa). There are obtained 13.6 g of (4S,5S)-4-methyl-5-phenyl-3-(2-methoxyphenylacetyl)oxazolidin-2-one in the form of a yellow oil. a solution, cooled to −78° C. obtained is finally added after returning to room temperature after separating the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of a saturated aqueous sodium chloride solution, dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a column of silica gel (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 80/20 by volume) and collecting 50 cm3 fractions concentrated to dryness under reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added, at room temperature, to a suspension of 1.89 g of sodium hydride (80% dispersion in vaseline) in 200 cm3 of dry tetrahydrofuran. This suspension is cooled to -30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to -78° C., which is obtained by adding 35.27 cm3 of a 1.6M solution of butyllithium in hexane to a solution, cooled to -78° C., of 10 g of (4S,5S)-4-methyl-5-phenyl-2-oxazolidinone in 200 cm3 of dry tetrahydrofuran, is finally added. The reaction mixture is stirred for 45 minutes at -30° C. and then after reequilibrating to room temperature, 200 cm3 of a saturated aqueous solution of ammonium chloride is added followed by 500 cm3 of ethyl acetate; after decantation, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous solution of sodium chloride, dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 and then 80/20 by volume) and collecting fractions of 50 cm3. Fractions 14 to 31 are pooled and concentrated to dryness under reduced pressure (2.7 kPa). 13.6 g of (4S,5S)-4-methyl5-Phenyl-3-(2-methoxyphenylacetyl)-2-oxazolidinone are obtained in the form of a yellow oil. a solution, cooled to -78° C. which is obtained is finally added after reequilibrating to room temperature after decantation, the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of a saturated aqueous solution of sodium chloride, dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 80/20 by volume) and collecting fractions of 50 cm3 concentrated to dryness under reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added, at room temperature, to a suspension of 1.89 g of sodium hydride (80% dispersion in vaseline) in 200 cm3 of dry tetrahydrofuran. This suspension is cooled to -30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to -78° C., which is obtained by adding 35.27 cm3 of a 1.6M solution of butyllithium in hexane to a solution, cooled to -78° C., of 10 g of (4S,5S)-4-methyl-5-phenyl-2-oxazolidinone in 200 cm3 of dry tetrahydrofuran, is finally added. The reaction mixture is stirred for 45 minutes at -30° C. and then after reequilibrating to room temperature, 200 cm3 of a saturated aqueous solution of ammonium chloride is added followed by 500 cm3 of ethyl acetate; after decantation, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous solution of sodium chloride, dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 and then 80/20 by volume) and collecting fractions of 50 cm3. Fractions 14 to 31 are pooled and concentrated to dryness under reduced pressure (2.7 kPa). 13.6 g of (4S,5S)-4-methyl5-Phenyl-3-(2-methoxyphenylacetyl)-2-oxazolidinone are obtained in the form of a yellow oil. a solution, cooled to -78° C. which is obtained is finally added after reequilibrating to room temperature after decantation, the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of a saturated aqueous solution of sodium chloride, dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 80/20 by volume) and collecting fractions of 50 cm3 concentrated to dryness under reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added to a suspension of 1.89 [lacuna] of sodium hydride (80% strength dispersion in liquid paraffin) in 200 cm3 of dry tetrahydrofuran at room temperature. This suspension is cooled to -30° C., 7.77 cm3 of pivaloyl chloride are added, and a solution, cooled to -78° C., obtained by adding a solution of 35.27 cm3 of 1.6M butyllithium in hexane to a solution, cooled to -78° C., of 10 g of (4S,5S)-4-methyl-5-phenyloxazolidin-2-one in 200 cm3 of dry tetrahydrofuran, is then finally added. The reaction mixture is stirred at -30° C. for 45 minutes and then, after returning to room temperature, 200 cm3 of an aqueous saturated solution of ammonium chloride and then 500 cm3 of ethyl acetate are added; after separation by settling, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of an aqueous saturated solution of sodium chloride, and is dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) by eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 and then 80/20 by volume) and collecting fractions of 50 cm3. Fractions 14 to 31 are combined and concentrated to dryness under-reduced pressure (2.7 kPa). 13.6 g of (4S,5S)-4-methyl-5-phenyl-3-(2-methoxyphenylacetyl)oxazolidin-2-one are obtained in the form of a yellow oil. a solution, cooled to -78° C. obtained is then finally added after returning to room temperature after separation the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of an aqueous saturated solution of sodium chloride, and is dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) by eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 80/20 by volume) and collecting fractions of 50 cm3 concentrated to dryness under-reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added at room temperature to a suspension of 1.89 g of sodium hydride (80% dispersion in petroleum jelly) in 200 cm3 of dry tetrahydrofuran. This suspension is cooled to −30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to −78° C., obtained by adding a solution of 35.27 cm3 of 1.6M butyllithium in hexane to a solution, cooled to −78° C., of 10 g of (4S,5S)-4-methyl-5-phenyloxazolidin-2-one in 200 cm3 of dry tetrahydrofuran is finally added. The reaction mixture is stirred for 45 minutes at −30° C. and then, after returning to room temperature, 200 cm3 of a saturated aqueous ammonium chloride solution and then 500 cm3 of ethyl acetate are added; after separating by settling, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous sodium chloride solution, dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a column of silica gel (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 and then 80/20 by volume) and collecting 50 cm3 fractions. Fractions 14 to 31 are combined and concentrated to dryness under reduced pressure (2.7 kPa). There are obtained 13.6 g of (4S,5S)-4-methyl-5-phenyl-3-(2-methoxyphenylacetyl)oxazolidin-2-one in the form of a yellow oil. a solution, cooled to −78° C. obtained is finally added after returning to room temperature after separating the organic phase is washed twice with 100 cm3 of water twice with 100 cm3 of a saturated aqueous sodium chloride solution, dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a column of silica gel (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a pressure of 0.6 bar of nitrogen with a mixture of cyclohexane and ethyl acetate (85/15 80/20 by volume) and collecting 50 cm3 fractions concentrated to dryness under reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added to a suspension of 1.89 g of sodium hydride (80% 25 dispersion in vaseline) in 200 cm3 of dry tetrahydrofuran, at room temperature. This suspension is cooled to -30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to -78° C., which is obtained by adding 35.27 cm3 of a 1.6M solution of butyllithium in hexane to a solution, cooled to -78° C., of 10 g of (4S,5S)-4-methyl-5-phenyl-2-oxazolidinone in 200 cm3 of dry tetrahydrofuran is finally added. The reaction mixture is stirred for 45 minutes at -30° C. and then after re-equilibrating to room temperature, 200 cm3 of a saturated aqueous solution of ammonium chloride are added followed by 500 cm3 of ethyl acetate; after decantation, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous solution of sodium chloride; dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 followed by 80/20 by volume) and collecting fractions of 50 cm3. Fractions 14 to 31 are pooled and concentrated to dryness under reduced pressure (2.7 kPa). 13.6 g of (4S,5S)-4-methyl-5-phenyl-3-(2-methoxyphenylacetyl)-2-oxazolidinone are obtained in the form of a yellow oil. a solution, cooled to -78° C. which is obtained is finally added after decantation, the organic phase is washed twice with 100 cm3 of water dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 followed by 80/20 by volume) collecting fractions of 50 cm3 concentrated to dryness under reduced pressure (2.7 kPa)

Conditions: temp:-30.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 9.38 g of 2-methoxyphenylacetic acid are added to a suspension of 1.89 g of sodium hydride (80% 25 dispersion in vaseline) in 200 cm3 of dry tetrahydrofuran, at room temperature. This suspension is cooled to -30° C., 7.77 cm3 of pivaloyl chloride are added and then a solution, cooled to -78° C., which is obtained by adding 35.27 cm3 of a 1.6M solution of butyllithium in hexane to a solution, cooled to -78° C., of 10 g of (4S,5S)-4-methyl-5-phenyl-2-oxazolidinone in 200 cm3 of dry tetrahydrofuran is finally added. The reaction mixture is stirred for 45 minutes at -30° C. and then after re-equilibrating to room temperature, 200 cm3 of a saturated aqueous solution of ammonium chloride are added followed by 500 cm3 of ethyl acetate; after decantation, the organic phase is washed twice with 100 cm3 of water and then twice with 100 cm3 of a saturated aqueous solution of sodium chloride; dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm), eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 followed by 80/20 by volume) and collecting fractions of 50 cm3. Fractions 14 to 31 are pooled and concentrated to dryness under reduced pressure (2.7 kPa). 13.6 g of (4S,5S)-4-methyl-5-phenyl-3-(2-methoxyphenylacetyl)-2-oxazolidinone are obtained in the form of a yellow oil. a solution, cooled to -78° C. which is obtained is finally added after decantation, the organic phase is washed twice with 100 cm3 of water dried over magnesium sulphate concentrated to dryness under reduced pressure (2.7 kPa) The residue is chromatographed on a silica gel column (particle size 0.04-0.06 mm, diameter 4.8 cm, height 36 cm) eluting under a nitrogen pressure of 0.6 bar with a cyclohexane and ethyl acetate mixture (85/15 followed by 80/20 by volume) collecting fractions of 50 cm3 concentrated to dryness under reduced pressure (2.7 kPa)