1-Azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid,6-[(1R)-1-[[(1,1-dimethylethyl)dimethylsilyl]oxy]ethyl]-4-methyl-7-oxo-3-[(phenylmethyl)thio]-, (4-nitrophenyl)methyl ester, (4R,5S,6S)-