At 10° C., 24 ml of diisopropylethylamine are added to 14 g of 3-[5-(tert-butyidimethyl-silanyloxy)-5-(4-fluorophenyl)pentanoyl]-4-phenyloxazolidin-2-one (10) and 12.5 g of 3-[(4-fluorophenylimino)methyl]benzonitrile 11 in 200 ml of methylene chloride, and 7.1 ml of trimethylsilyl chloride are added dropwise. After 1 h, 3.4 ml of titanium tetrachloride are added dropwise at −10° C. The mixture is stirred at −10° C. for 3 h and then allowed to stand at −30° C. for another 12 h. 8 ml of acetic acid and 140 ml of a 7% strength aqueous tartaric acid solution are then added, and stirring is continued at room temperature for another 2 h. 50 ml of 20% strength aqueous sodium hydrogen sulfite solution are added, and the mixture is then stirred for another hour and extracted with methylene chloride. The organic phase is dried over magnesium sulfate, concentrated and purified by silica gel chromatography (ethyl acetate/heptane=1/3→1/1). This gives 12
