(R)-3-Acetoxymethyl-7-[1-bromo-meth-(E)-ylidene]-5,5,8-trioxo-5λ6-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid benzhydryl ester

(6R)-3-acetoxymethyl-7t-(4-nitro-benzylideneamino)-8-oxo-(6rH)-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid benzhydryl ester

(6R,7R)-7-Allyloxycarbonylamino-8-oxo-3-(1,2,2,2-tetrachloro-ethoxycarbonyloxymethyl)-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid benzhydryl ester

(R)-3-Acetoxymethyl-8-oxo-7-[1-pyridin-2-yl-meth-(Z)-ylidene]-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid benzhydryl ester

(6R,7R)-3-acetyloxymethyl-7-<2-(2-methoxyphenyl)-4-thiazolyl>acetylamino-8-oxo-5-thia-1-azabicyclo<4.2.0>oct-2-ene-2-carboxylic acid diphenylmethyl ester