Reaction SMILES: C(Cl)(Cl)=O.[CH3:5][O:6][N:7]=[C:8]([C:12]1[N:13]=[C:14]([NH:17][C:18]([C:31]2[CH:36]=[CH:35][CH:34]=[CH:33][CH:32]=2)([C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=2)[C:19]2[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=2)[S:15][CH:16]=1)[C:9](O)=[O:10].[NH2:37][CH:38]1[C:45](=[O:46])[N:44]2[CH:39]1[S:40](=[O:74])[CH2:41][C:42]([C:63]1[S:67][C:66]([C:68]3[CH:69]=[N:70][CH:71]=[CH:72][CH:73]=3)=[N:65][CH:64]=1)=[C:43]2[C:47]([O:49][CH:50]([C:57]1[CH:62]=[CH:61][CH:60]=[CH:59][CH:58]=1)[C:51]1[CH:56]=[CH:55][CH:54]=[CH:53][CH:52]=1)=[O:48].C(=O)(O)[O-].[Na+]>C1(C)C=CC=CC=1.C(Cl)Cl.CN(C)C(=O)C>[CH:50]([O:49][C:47]([C:43]1[N:44]2[CH:39]([S:40](=[O:74])[CH2:41][C:42]=1[C:63]1[S:67][C:66]([C:68]3[CH:69]=[N:70][CH:71]=[CH:72][CH:73]=3)=[N:65][CH:64]=1)[CH:38]([NH:37][C:9](=[O:10])[C:8](=[N:7][O:6][CH3:5])[C:12]1[N:13]=[C:14]([NH:17][C:18]([C:25]3[CH:26]=[CH:27][CH:28]=[CH:29][CH:30]=3)([C:31]3[CH:36]=[CH:35][CH:34]=[CH:33][CH:32]=3)[C:19]3[CH:20]=[CH:21][CH:22]=[CH:23][CH:24]=3)[S:15][CH:16]=1)[C:45]2=[O:46])=[O:48])([C:57]1[CH:58]=[CH:59][CH:60]=[CH:61][CH:62]=1)[C:51]1[CH:56]=[CH:55][CH:54]=[CH:53][CH:52]=1
Reactant: NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(c3cnc(-c4cccnc4)s3)CS(=O)C12
Reactant: CON=C(C(=O)O)c1csc(NC(c2ccccc2)(c2ccccc2)c2ccccc2)n1
Agent: O=C(Cl)Cl
Agent: O=C([O-])O
Agent: [Na+]
Solvent: ClCCl
Solvent: Cc1ccccc1
Solvent: CC(=O)N(C)C
Product: CON=C(C(=O)NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(c3cnc(-c4cccnc4)s3)CS(=O)C12)c1csc(NC(c2ccccc2)(c2ccccc2)c2ccccc2)n1
Temperature: -10 °C
Reaction time: 0.5 h
Yield: 43.5 %

Procedure:
A 2 M solution of phosgene in toluene (32.6 cc) is added dropwise to a solution of the syn form of 2-methoxyimino-2-(2-tritylaminothiazol-4-yl)-acetic acid (25 g) in a mixture of dry methylene chloride (500 cc) and N,N-dimethylacetamide (5.25 cc), cooled to -10° C. The reaction mixture is stirred for 3 hours 30 minutes at between -5° and 0° C. and N,N-dimethylacetamide (15.8 cc) and a solution of 7-amino-2-benzhydryloxycarbonyl-8-oxo-3-[2-(pyridin-3-yl)-thiazol-5-yl]-5-thia-1-azabicyclo-[4.2.0]oct-2-ene 5-oxide (26 g) in methylene chloride (200 cc) are then added at -5° C. The reaction mixture is stirred for 1 hour 30 minutes at between 0° and +5° C. and then for 16 hours at 20° C. and is then treated with a 5% strength solution of sodium bicarbonate (500 cc) and filtered. The organic phase is washed with a semi-saturated solution of sodium chloride (500 cc), dried over magnesium sulphate and concentrated to dryness under reduced pressure (30 mm Hg; 4 kPa) at 30° C. The residue is chromatographed on a column (height=52 cm, diameter=7 cm) of silica gel (0.06-0.2 mm), ethyl acetate being used as the eluent and 1 liter fractions being collected. Fractions 6 to 13 are combined and concentrated to dryness under reduced pressure (30 mm Hg; 4 kPa) at 30° C. to give the syn isomer of 2-benzhydryloxycarbonyl-7-[2-methoxyimino-2-(2-tritylaminothiazol-4-yl)-acetamido]-8-oxo-3-[2-(pyridin-3-yl)-thiazol-5-yl]-5-thia-1-azabicyclo[4.2 .0]-oct-2-ene 5-oxide (20.2 g) in the form of a cream solid (by taking up the resulting hard foam in methylene chloride (80 cc) and precipitating the product with isopropyl ether (300 cc)).