A solution of benzyl acetate (0.011 mol) in anhydrous tetrahydrofuran (5 ml) is added dropwise to solution of lithium diisopropylamide (0.011 mol) in anhydrous tetrahydrofuran (20 ml) at -78° C. After stirring 15 more min at -78° C. the reaction mixture is treated dropwise with a solution of N-(t-butyldimethylsilyl)-3-azido-4-(2-oxoethyl)-azetidin-2-one (0.01 mol) in tetrahydrofuran (10 ml). The mixture is stirred at -78° an additional 15 min and then quenched with 2.5 N hydrochloric acid (10 ml). The mixture is diluted with ethyl acetate, washed with water, 5% sodium bicarbonate solution, and brine, dried with magnesium sulfate, and evaporated under vacuum to afford N-(t-butyldimethylsilyl)-3-azido-4-(3-benzyloxycarbonyl-2-hydroxypropyl)-azetidin-2-one.
