A stirred solution of (R)-4-(1-hydroxy-1-methyl-2-phenyl-ethyl)-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester (0.50 g) in THF (25 ml) was cooled under an argon atmosphere to −78° C. and treated dropwise with 1 M lithium-bis-(trimethylsilyl)amide in THF (1.79 ml). The solution was allowed to warm to r.t. Then, phenyl chlorothionoformate (0.3 ml) was added. After stirring at r.t. for 2 hrs, the reaction mixture was quenched with saturated aqueous NH4Cl solution and extracted with EtOAc. The organic layer was washed with brine, dried over MgSO4 and concentrated to give crude (R)-2,2-dimethyl-4-(1-methyl-1-phenoxythiocarbonyloxy-2-phenyl-ethyl)-oxazoli-dine-3-carboxylic acid tert-butyl ester as pale yellow oil which was used in the next reaction step without further purification.
