To a solution of phenol (2.82 g 30 mmole) in THF (30 ml) and 1N NaOH (26 ml, 26 mmole), (3S, 4S)-3-benzyloxycarbonylamino-4-acetoxy-azetidin-2-one (5.56 g, 20 mmole) in THF (40 ml) and H2O (20 ml) is added at 0° C. The mixture is stirred at 0° C for 1 hour and then at room temperature for 30 min. After removal of solvent, the residue is dissolved in ethyl acetate, washed with water, brine and dried over sodium sulphate. After removal of solvent, the residue is purified by silica gel column chromatography using hexane-ethyl acetate as eluent. 2.75 g of (3S, 4S)-3-benzyloxycarbonylamino-4-phenoxy-azetidin-2-one (A), 890 mg of (3S, 4R)-3-benzyloxycarbonylamino-4-phenoxy-azetidin-2-one (B) and 1.08 g of a mixture of (A) and (B) is obtained.
