(4S,6R,7S)-4-Acetoxy-7-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-8-oxo-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid 4-nitro-benzyl ester

(2S,5R,6S)-6-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-3-[1-(4-fluoro-benzenesulfonyl)-meth-(Z)-ylidene]-7-oxo-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid 4-nitro-benzyl ester