Under a nitrogen atmosphere and at 0° C., 87.78 ml. of 1.5M. n-butyllithium/hexane (132 mmoles) is added dropwise to 18.49 ml. (132 mmoles) of diisopropylamine in 150 ml. of dry tetrahydrofuran, and the mixture is stirred for 30 minutes to form a solution of lithium diisopropylamide. The obtained solution is cooled to -70° C., a solution of 17.76 ml. (132 mmoles) of t-butyl acetate in 25 ml. of dry tetrahydrofuran is added over a period of 1 hour with stirring at -65°--70° C., the reaction mixture is stirred for 1.5 hours at the same temperature, a solution of 11.28 g. (30 mmoles) of methyl (S)-3-hydroxy-4-(triphenylmethoxy)butanoate (obtainable by Step 3 of Example 1) in 75 ml. of dry tetrahydrofuran is added to the obtained solution of t-butyl lithioacetate at -65°--70° C., and the yellow solution is stirred at about - 70° C. for 0.5 hour, warmed to -10° C. and stirred at -10° C. for 1 hour (with thin layer chromatography (TLC) monitoring to indicate when the reaction is over), the reaction mixture being stirred under nitrogen throughout. 150 ml. of saturated aqueous ammonium chloride is added to quench the reaction at -60°--70° C., the mixture is warmed to 0° C., transferred to a separatory funnel and diluted with ethyl acetate, and the organic phase is separated. The aqueous layer is extracted with an additional 200 ml. of ethyl acetate, and the organic phases are combined, washed successively with 90 ml. of 1N. hydrochloric acid and 90 ml. of saturated aqueous sodium bicarbonate, dried and filtered. The organic solution is evaporated to yield the crude product (17.43 g.) (estimated to be about 80% pure by chromatography analysis).
