Reaction SMILES: [N:1]1[CH:6]=[CH:5][CH:4]=[C:3]([NH:7][C:8]([NH2:10])=[S:9])[CH:2]=1.[CH:11]([O:24][C:25]([C:27]1[N:28]2[CH:31]([S:32][CH2:33][C:34]=1[CH:35](Br)[CH:36]=O)[CH:30]([NH:39][C:40](=[O:79])[C:41](=[N:67][O:68][C:69]([C:72]([O:74][C:75]([CH3:78])([CH3:77])[CH3:76])=[O:73])([CH3:71])[CH3:70])[C:42]1[N:43]=[C:44]([NH:47][C:48]([C:61]3[CH:66]=[CH:65][CH:64]=[CH:63][CH:62]=3)([C:55]3[CH:60]=[CH:59][CH:58]=[CH:57][CH:56]=3)[C:49]3[CH:54]=[CH:53][CH:52]=[CH:51][CH:50]=3)[S:45][CH:46]=1)[C:29]2=[O:80])=[O:26])([C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1)[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1.N1C=CC=CC=1.Cl>O1CCCC1.C(OCC)(=O)C.O>[CH:11]([O:24][C:25]([C:27]1[N:28]2[CH:31]([S:32][CH2:33][C:34]=1[C:35]1[S:9][C:8]([NH:7][C:3]3[CH:2]=[N:1][CH:6]=[CH:5][CH:4]=3)=[N:10][CH:36]=1)[CH:30]([NH:39][C:40](=[O:79])[C:41](=[N:67][O:68][C:69]([C:72]([O:74][C:75]([CH3:78])([CH3:77])[CH3:76])=[O:73])([CH3:70])[CH3:71])[C:42]1[N:43]=[C:44]([NH:47][C:48]([C:55]3[CH:60]=[CH:59][CH:58]=[CH:57][CH:56]=3)([C:49]3[CH:54]=[CH:53][CH:52]=[CH:51][CH:50]=3)[C:61]3[CH:62]=[CH:63][CH:64]=[CH:65][CH:66]=3)[S:45][CH:46]=1)[C:29]2=[O:80])=[O:26])([C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1)[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1
Reactant: CC(C)(C)OC(=O)C(C)(C)ON=C(C(=O)NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(C(Br)C=O)CSC12)c1csc(NC(c2ccccc2)(c2ccccc2)c2ccccc2)n1
Reactant: NC(=S)Nc1cccnc1
Agent: Cl
Solvent: c1ccncc1
Solvent: O
Solvent: CCOC(C)=O
Product: CC(C)(C)OC(=O)C(C)(C)ON=C(C(=O)NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(c3cnc(Nc4cccnc4)s3)CSC12)c1csc(NC(c2ccccc2)(c2ccccc2)c2ccccc2)n1
Temperature: 25 °C
Reaction time: 0.58 h

Procedure:
A mixture of (pyridin-3-yl)-thiourea (0.08 g) and the syn isomer of 2-benzhydryloxycarbonyl-3-(1-bromo-2-oxoethyl)-7-[2-(2-t-butoxycarbonylprop-2-yl-oxyimino)-2-(2-tritylaminothiazol-4-yl)-acetamido]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene (mixture of the two diastereoisomers in respect of the substituent in the 3-position) (0.55 g) in tetrahydrofuran (10 cc) is stirred for 35 minutes at 25° C. and then treated with pyridine (0.042 cc) and water (1 cc). The reaction mixture is stirred for 16 hours at 25° C. and then poured into a mixture of ethyl acetate (50 cc) and 0.2 N hydrochloric acid (50 cc). The organic solution is washed with a saturated solution of sodium bicarbonate (50 cc), water (3×50 cc) and then with a saturated solution of sodium chloride (20 cc) and dried over magnesium sulphate. The residue obtained after evaporation of the solvent to dryness under reduced pressure (4 kPa) at 30° C. is chromatographed on a column (height: 24 cm, diameter: 2 cm) containing silica gel (0.04-0.06 mm), elution being carried out under a pressure of 0.5 bar (50 kPa) with a mixture of cyclohexane and ethyl acetate (15/85 by volume) and 15 cc fractions being collected. Fractions 7 to 13 are combined and concentrated to dryness under reduced pressure (4 kPa) at 30° C. to give the syn isomer of 2-benzhydryloxycarbonyl-7-[2-(2-t-butoxycarbonylprop-2-yl-oxyimino)-2-(2-tritylaminothiazol-4-yl)-acetamido]-8-oxo-3-[2-(pyridin-3-yl-amino)-thiazol-5-yl]-5-thia-1-azabicyclo[4.2.0]oct-2-ene (0.39 g) in the form of a hard yellow foam.