Reaction SMILES: [CH3:1][O:2][N:3]=[C:4]([C:8]1[N:9]=[C:10]([NH:13][C:14]([C:27]2[CH:32]=[CH:31][CH:30]=[CH:29][CH:28]=2)([C:21]2[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=2)[C:15]2[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=2)[S:11][CH:12]=1)[C:5](O)=[O:6].ON1C2C=CC=CC=2N=N1.[NH2:43][CH:44]1[C:51](=[O:52])[N:50]2[CH:45]1[S:46][CH2:47][C:48]([C:69]1[S:73][C:72]([CH2:74][C:75]3[CH:76]=[N:77][CH:78]=[CH:79][CH:80]=3)=[N:71][CH:70]=1)=[C:49]2[C:53]([O:55][CH:56]([C:63]1[CH:68]=[CH:67][CH:66]=[CH:65][CH:64]=1)[C:57]1[CH:62]=[CH:61][CH:60]=[CH:59][CH:58]=1)=[O:54].C(O)(=O)C>CN(C)C=O>[CH:56]([O:55][C:53]([C:49]1[N:50]2[CH:45]([S:46][CH2:47][C:48]=1[C:69]1[S:73][C:72]([CH2:74][C:75]3[CH:76]=[N:77][CH:78]=[CH:79][CH:80]=3)=[N:71][CH:70]=1)[CH:44]([NH:43][C:5](=[O:6])[C:4](=[N:3][O:2][CH3:1])[C:8]1[N:9]=[C:10]([NH:13][C:14]([C:21]3[CH:22]=[CH:23][CH:24]=[CH:25][CH:26]=3)([C:27]3[CH:32]=[CH:31][CH:30]=[CH:29][CH:28]=3)[C:15]3[CH:16]=[CH:17][CH:18]=[CH:19][CH:20]=3)[S:11][CH:12]=1)[C:51]2=[O:52])=[O:54])([C:63]1[CH:64]=[CH:65][CH:66]=[CH:67][CH:68]=1)[C:57]1[CH:62]=[CH:61][CH:60]=[CH:59][CH:58]=1
Reactant: CON=C(C(=O)O)c1csc(NC(c2ccccc2)(c2ccccc2)c2ccccc2)n1
Reactant: NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(c3cnc(Cc4cccnc4)s3)CSC12
Agent: On1nnc2ccccc21
Solvent: CC(=O)O
Solvent: CN(C)C=O
Product: CON=C(C(=O)NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(c3cnc(Cc4cccnc4)s3)CSC12)c1csc(NC(c2ccccc2)(c2ccccc2)c2ccccc2)n1
Temperature: 5 °C
Reaction time: 1 h
Yield: 56.3 %

Procedure:
The syn isomer of 2-methoxyimino-2-(2-tritylaminothiazol-4-yl)-acetic acid (5.32 g), 3-hydroxybenzotriazole (1.62 g) and N,N-dicyclohexylcarbodiimide (2.47 g) are added to a solution, cooled to +5° C., of 7-amino-2-benzhydryloxycarbonyl-8-oxo-3-[2-(pyridin-3-yl-methyl)-thiazol-5-yl]-5-thia-1-azabicyclo[4.2.0]oct-2-ene (5.4 g) in N,N-dimethylformamide (100 cc). The mixture is stirred for 1 hour at 5° C., the temperature is then allowed to rise and the mixture is stirred for 4 hours at 23° C. Acetic acid (0.5 cc) is added, the mixture is stirred for 5 minutes and the suspension is filtered. The filtrate is poured into a 50/50 (by volume) mixture of water and ethyl acetate (500 cc). The organic phase is decanted and then washed successively with a 0.1 N solution of hydrochloric acid (100 cc), a saturated solution of sodium bicarbonate (100 cc), distilled water (100 cc) and a saturated solution of sodium chloride (100 cc). It is dried over anhydrous sodium sulphate and filtered and the filtrate is concentrated to dryness under reduced pressure (20 mm Hg; 2.7 kPa) at 30° C. The residue is purified by chromatography on silica gel (0.05-0.2 mm) (height of silica: 77 cm, diameter of the column: 3.5 cm), elution being carried out with a 20/80 (by volume) mixture of cyclohexane and ethyl acetate (1 liter) and then with a 10/90 (by volume) mixture of cyclohexane and ethyl acetate (3.8 liters) and 60 cc fractions being collected. Fractions 39 to 80 are combined and concentrated to dryness under reduced pressure (20 mm Hg; 2.7 kPa). This gives the syn isomer of 2-benzhydryloxycarbonyl-7-[2-methoxyimino-2-(2-tritylaminothiazol-4-yl)-acetamido]-8-oxo-3-[2-(pyridin-3-yl-methyl)thiazol-5-yl]-5-thia-1-azabicyclo[4.2.0]oct-2-ene (5.43 g) in the form of a hard yellow foam.