(5S,6R,7R)-7-Acetylamino-4-(chloro-phenylsulfanyl-methyl)-3-methyl-5,8-dioxo-5λ4-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid 2,2,2-trichloro-ethyl ester 在
silica gel 作用下,
以98%的产率得到(5S,6R,7R)-7-Acetylamino-4-[1-chloro-meth-(Z)-ylidene]-3-methyl-5,8-dioxo-5λ
4-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid 2,2,2-trichloro-ethyl ester