(5S,6R,7R)-7-Acetylamino-4-[1-chloro-meth-(Z)-ylidene]-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   、                                                                                      alkaline earth salt of/the/ methylsulfuric acid                                                                                                                                                                                                                                                                                                          以48%的产率得到(5S,6R,7R)-7-Acetylamino-3-methyl-5,8-dioxo-4-pent-(Z)-ylidene-5λ
4-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid 2,2,2-trichloro-ethyl ester