t-butyl 3-acetoxymethyl-7α-methoxy-2-methylene-3-cephem-4-carboxylate 1,1-dioxide

(6R,7S)-3-Acetoxymethyl-7-methoxy-5,5,8-trioxo-5λ6-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid isopropyl ester

(6R,7S)-3-Acetoxymethyl-7-methoxy-5,5,8-trioxo-5λ6-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid benzyl ester