Chloral → (4S,5R)-5-methoxycarbonyl-4-phenyl-2-trichloromethyl-1,3-oxazolidine

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A solution of 3.0 g of methyl (2R,3S)-3-(tert-butoxycarbonylamino)-2-hydroxy-3-phenylpropionate, of 5 cm3 of chloral and of 0.05 g of pyridinium p-toluenesulphonate in 40 cm3 of anhydrous toluene is heated at reflux with distillation of the solvent. 15 cm3 of solvent are distilled and then 5 cm3 of chloral and 0.05 g of pyridinium p-toluenesulphonate are added. 20 cm3 of solvent are distilled and then 5 cm3 of chloral as well as 30 cm3 of anhydrous toluene are added. 25 cm3 of solvent are distilled and 5 cm3 of chloral and 35 cm3 of anhydrous toluene are added. 25 cm3 of solvent are distilled and then the solution is cooled to a temperature in the region of 20° C. The organic solution is washed with water (2 times 50 cm3), dried over sodium sulphate and concentrated to dryness under reduced pressure at approximately 50° C. The residue obtained is purified by liquid chromatography on silica gel, the eluent being an ethyl acetate/cyclohexane (1/3 by volume) mixture. There are thus obtained, with a yield of 91%, 3.0 g of (4S,5R)-5-methoxycarbonyl-4-phenyl-2-trichloromethyl-1,3-oxazolidine whose characteristics are the following:

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