Reaction SMILES: C1(C)C=CC(S(O)(=O)=O)=CC=1.[CH:12]([O:25][C:26]([C:28]1[N:29]2[CH:32]([S:33](=[O:39])[CH2:34][C:35]=1[CH:36]=[CH:37][Cl:38])[CH:31]([NH:40]C(OC(C)(C)C)=O)[C:30]2=[O:48])=[O:27])([C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)[C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=1>C(#N)C>[NH2:40][CH:31]1[C:30](=[O:48])[N:29]2[CH:32]1[S:33](=[O:39])[CH2:34][C:35]([CH:36]=[CH:37][Cl:38])=[C:28]2[C:26]([O:25][CH:12]([C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=1)[C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)=[O:27]
Reactant: CC(C)(C)OC(=O)NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(C=CCl)CS(=O)C12
Agent: Cc1ccc(S(=O)(=O)O)cc1
Solvent: CC#N
Product: NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(C=CCl)CS(=O)C12
Reaction time: 0.5 h
Yield: 90.1 %

Procedure:
A solution of para-toluenesulphonic acid (hydrate) (2.2 g) in acetonitrile (15 cc) is added, in the course of 15 minutes, to a solution of the E form of 2-benzhydryloxycarbonyl-7-t-butoxycarbonylamino-3-(2-chlorovinyl)-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-5-oxide (product 12c) (3.4 g) in acetonitrile (15 cc) at 40° C. After 30 minutes at 40° C., the reaction mixture is concentrated to dryness under reduced pressure (30 mm Hg; 4 kPa) at 30° C. The residue is taken up in ethyl acetate (100 cc) and the solution obtained is washed with a saturated solution of sodium bicarbonate (2×50 cc) and distilled water (2×50 cc) and then dried over sodium sulphate and concentrated to dryness under reduced pressure (30 mm Hg; 4 kPa) at 35° C. The residue is dried under reduced pressure (0.2 mm Hg; 0.03 kPa) at 25° C. for 1 hour. This yields crude E form of 7-amino-2-benzhydryloxycarbonyl-3-(2-chlorovinyl)-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-5-oxide (product 12d) (2.5 g) in the form of a hard orange foam. This product is redissolved in dry methylene chloride (45 cc), a solution of 2-methoxyimino-2-(2-tritylaminothiazol-4-yl)acetic acid (syn isomer) (2.5 g) and 4-dimethylaminopyridine (0.03 g) in dry methylene chloride (30 cc) is added and N,N'-dicyclohexylcarbodiimide (1.3 g) and dry methylene chloride (10 cc) are then added (after cooling to about 4° C.) The reaction mixture is stirred for 40 minutes at about 6° C. and then 16 hours at 25° C. The precipitate of N,N'-dicyclohexylurea is filtered off and rinsed with dry methylene chloride (2×5 cc). The filtrate and the combined washings are concentrated to dryness under reduced pressure (30 mm Hg; 4 kPa) at 30° C. and the residue obtained is taken up in ethyl acetate (200 cc). The solution obtained is washed successively with 0.2 N hydrochloric acid (50 cc), a semisaturated solution of sodium bicarbonate (2×50 cc) and a saturated solution of sodium chloride (50 cc) and then dried over sodium sulphate. The residue obtained after evaporation to dryness under reduced pressure (30 mm Hg; 4 kPa) at 30° C. is chromatographed on a column of silica (0.04-0.06) (diameter of the column: 4 cm, height: 30 cm), elution being carried out with methylene chloride (800 cc) and then with a mixture of methylene chloride and ethyl acetate (95/5 by volume) (1,200 cc) under a pressure of 50 kPa, and 60 cc fractions being collected. Fractions 12 to 25, containing the pure product, are combined and concentrated to dryness under reduced pressure. This yields a product (12a) (1.7 g) in the form of a hard cream-coloured foam.