[C:1]([O:5][C:6](=[O:57])[C:7]([O:10]/[N:11]=[C:12](/[C:43]1[N:44]=[C:45]([NH:49][C:50]([O:52][C:53]([CH3:56])([CH3:55])[CH3:54])=[O:51])[S:46][C:47]=1[Cl:48])\[C:13]([NH:15][C@@H:16]1[C:23](=[O:24])[N:22]2[C@@H:17]1[S:18][CH2:19][C:20]([CH2:41][Cl:42])=[C:21]2[C:25]([O:27][CH:28]([C:35]1[CH:40]=[CH:39][CH:38]=[CH:37][CH:36]=1)[C:29]1[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=1)=[O:26])=[O:14])([CH3:9])[CH3:8])([CH3:4])([CH3:3])[CH3:2].C1C=C(Cl)C=C(C(OO)=[O:66])C=1.[O-]S([O-])(=S)=O.[Na+].[Na+]>ClCCl>[C:1]([O:5][C:6](=[O:57])[C:7]([O:10]/[N:11]=[C:12](/[C:43]1[N:44]=[C:45]([NH:49][C:50]([O:52][C:53]([CH3:56])([CH3:55])[CH3:54])=[O:51])[S:46][C:47]=1[Cl:48])\[C:13]([NH:15][C@@H:16]1[C:23](=[O:24])[N:22]2[C@@H:17]1[S@:18](=[O:66])[CH2:19][C:20]([CH2:41][Cl:42])=[C:21]2[C:25]([O:27][CH:28]([C:35]1[CH:40]=[CH:39][CH:38]=[CH:37][CH:36]=1)[C:29]1[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=1)=[O:26])=[O:14])([CH3:8])[CH3:9])([CH3:2])([CH3:3])[CH3:4]To a solution of (6R,7R)-benzhydryl 7-((Z)-2-(((1-(tert-butoxy)-2-methyl-1-oxopropan-2-yl)oxy)imino)-2-(2-((tert-butoxycarbonyl)amino)-5-chlorothiazol-4-yl)acetamido)-3-(chloromethyl)-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate (29.9 g, 34.7 mmol) in Dichloromethane (DCM) (1.1 L) at −40° C. was added dropwise a solution of m-CPBA (8.17 g, 36.5 mmol) in Dichloromethane (DCM) (220 mL) over 10 min. The mixture was stirred at the same temperature over 30 min. LCMS indicated completion of the reaction. The mixture was treated with 15% aq. Na2S2O3 (200 mL). The organic phase was separated and washed with 5% NaHCO3 (400 mL), brine (400 mL), dried (Na2SO4), filtered, and concentrated. The residue was purified by CombiFlash automated silica gel chromatography (330 g column, 0-50% EtOAc/Hexanes) to afford (5R,6R,7R)-benzhydryl 7-((Z)-2-(((1-(tert-butoxy)-2-methyl-1-oxopropan-2-yl)oxy)imino)-2-(2-((tert-butoxycarbonyl)amino)-5-chlorothiazol-4-yl)acetamido)-3-(chloromethyl)-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate 5-oxide (29 g, 31.8 mmol, 91% yield) as a light yellow solid. LCMS: (M+H)+: 876.3
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