Reaction SMILES: [P:1]([O:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)([O:9][C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1)[O:2][C:3]1[CH:8]=[CH:7][CH:6]=[CH:5][CH:4]=1.[Cl:23][Cl:24].[CH:25]([O:38][C:39]([C:41]1[N:42]2[CH:45]([S:46][CH2:47][C:48]=1[CH2:49]C=O)[CH:44]([NH:52][C:53]([O:55][C:56]([CH3:59])([CH3:58])[CH3:57])=[O:54])[C:43]2=[O:60])=[O:40])([C:32]1[CH:37]=[CH:36][CH:35]=[CH:34][CH:33]=1)[C:26]1[CH:31]=[CH:30][CH:29]=[CH:28][CH:27]=1.N1C=CC=CC=1.[CH2:67]([Cl:69])[Cl:68]>>[Cl:23][Cl:24].[P:1]([O:9][C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1)([O:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)[O:2][C:3]1[CH:4]=[CH:5][CH:6]=[CH:7][CH:8]=1.[CH:25]([O:38][C:39]([C:41]1[N:42]2[CH:45]([S:46][CH2:47][C:48]=1[CH2:49][CH:67]([Cl:69])[Cl:68])[CH:44]([NH:52][C:53]([O:55][C:56]([CH3:59])([CH3:58])[CH3:57])=[O:54])[C:43]2=[O:60])=[O:40])([C:26]1[CH:27]=[CH:28][CH:29]=[CH:30][CH:31]=1)[C:32]1[CH:37]=[CH:36][CH:35]=[CH:34][CH:33]=1
Reactant: CC(C)(C)OC(=O)NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(CC=O)CSC12
Reactant: ClCCl
Agent: ClCl
Agent: c1ccc(OP(Oc2ccccc2)Oc2ccccc2)cc1
Solvent: c1ccncc1
Product: CC(C)(C)OC(=O)NC1C(=O)N2C(C(=O)OC(c3ccccc3)c3ccccc3)=C(CC(Cl)Cl)CSC12

Procedure:
A solution of the addition compound of chlorine and triphenyl phosphite is prepared by adding a solution of triphenyl phosphite (1.55 g) in methylene chloride (5 cc), in the course of 15 minutes, to a 10% strength (weight/volume) solution of chlorine in methylene chloride (4 cc), cooled to -5° C. This solution is added in the course of 90 minutes, at -10° C., to a solution of 2-benzhydryloxycarbonyl-7-t-butoxycarbonylamino-8-oxo-3-(2-oxoethyl)-5-thia-1-azabicyclo[4.2.0]oct-2-ene (product 11 g) (2.4 g) and pyridine (0.4 cc) in methylene chloride (15 cc). The reaction mixture is washed with distilled water (20 cc), a saturated solution of sodium bicarbonate (20 cc) and distilled water (2×20 cc) and then dried over magnesium sulphate and concentrated to dryness under reduced pressure (30 mm Hg; 4 kPa) at 30° C. This yields an equimolecular mixture (4.6 g) of 2-benzhydryloxycarbonyl-7-t-butoxycarbonylamino-3-(2,2-dichloroethyl)-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene (product 11h) and triphenyl phosphate. This mixture can be used for the remainder of the synthesis, without additional purification, by redissolving it in dry methylene chloride (15 cc) and by adding a solution of 85% pure metachloroperbenzoic acid (1.22 g) in methylene chloride (30 cc), in the course of 20 minutes, to the above solution, cooled to -10° C. The insoluble material is removed by filtration and the filtrate is washed with a saturated solution of sodium bicarbonate (2×25 cc) and a saturated solution of sodium chloride (2×25 cc) and then dried over magnesium sulphate. The residue obtained after the solvent has been evaporated off under reduced pressure (30 mm Hg; 4 kPa) at 35° C. is chromatographed on a column of silica (0.04-0.06) (diameter of the column: 2 cm; height: 30 cm), elution being carried out with a mixture of cyclohexane and ethyl acetate (60/40 by volume) under 50 kPa, and 30 cc fractions being collected. Fractions 6 to 12 are combined and concentrated to dryness under reduced pressure (30 mm Hg; 4 kPa) at 40° C. This yields a hard yellow foam (1.3 g) mainly consisting of product (11f).