(R)-3-((E)-2-tert-Butoxycarbonyl-vinyl)-4-methylene-5,5,8-trioxo-7-[1-pyridin-2-yl-meth-(Z)-ylidene]-5λ6-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid benzhydryl ester