[C:1]1([CH2:7][O:8][C:9]([NH:11][C@H:12]2[CH2:15][NH:14][C:13]2=[O:16])=[O:10])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[C:17](Cl)([Cl:19])=[O:18].C1(C)C=CC=CC=1>ClCCl>[Cl:19][C:17]([N:14]1[CH2:15][C@H:12]([NH:11][C:9]([O:8][CH2:7][C:1]2[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=2)=[O:10])[C:13]1=[O:16])=[O:18](S)-3-[[(Phenylmethoxy)carbonyl]amino]-2-azetidinone was suspended in 5 ml of dichloromethane and cooled to -10° C. A solution of 12.5% phosgene in toluene (2.9 ml, 3.4 mmol) was added dropwise to the rapidly stirring mixture. After stirring at -10° C. for 2 hours, the volatiles were evaporated without external heating. The residue was cooled to -10° C. and dissolved in 5 ml of dichloromethane to give (S)-1-chlorocarbonyl-3-[[(phenylmethoxy)carbonyl]amino]-2-azetidinone. The compound was not characterized, but was used as a crude intermediate.
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