p-nitrobenzyl 2-<(3S,4R)-3-<(1R)-(tert-butyldimethylsiloxy)ethyl>-4-(ethoxyacetylthio)-2-oxoazetidin-1-yl>-2-triphenylphosphoranylideneacetate

(2S,5R,6S)-6-Bromo-6-[1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-3,3-dimethyl-7-oxo-4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid methyl ester