C1(OC)C=CC=CC=1.[Cl-].[Al+3].[Cl-].[Cl-].[C:13]([O:16][C@@H:17]1[NH:20][C:19](=[O:21])[C@H:18]1[NH2:22])(=[O:15])[CH3:14].C(N(CC)CC)C.[C:30]1([CH2:36][C:37](Cl)=[O:38])[CH:35]=[CH:34][CH:33]=[CH:32][CH:31]=1>C(OCC)(=O)C.C(OCC)(=O)C.CO>[C:13]([O:16][C@@H:17]1[NH:20][C:19](=[O:21])[C@H:18]1[NH:22][C:37](=[O:38])[CH2:36][C:30]1[CH:35]=[CH:34][CH:33]=[CH:32][CH:31]=1)(=[O:15])[CH3:14]To a solution of 0.55 g (2 moles) of (3S,4S)-4-acetoxy-3-benzyl oxycarbonylamino-azetidin-2-one in 2 ml of anisole 0.40 g (3 mmoles) of anhydrous aluminum chloride are added at 20° C., by controlling the reaction by TLC (eluent: ethyl acetate/methanol=95/5 v/v). When the reaction is over, the mixture is filtered off and the filtered solution is concentrated under vacuum to obtain a residue of 0.260 g consisting of crude (3S,4S)-4-acetoxy-3-amino-azetidin-2-one. The residue is taken up with 30 ml of ethyl acetate and to the resulting solution 0.31 g (3 moles) of triethylamine and, afterwards, 0.695 g (4.5 mmoles) of phenylacetyl chloride are added. The mixture is stirred for 6 hours at 20°÷25° C., then it is concentrated under vacuum to obtain a residue which is taken up with ethyl acetate and subjected to a purification on a silica gel column (eluent: ethyl acetate). Thus, 0.165 g of (3S,4S)-4-acetoxy-3-phenylacetamido-azetidin-2-one (II) is obtained.
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