(R)-(-)-5-phenyl-1,3-dioxolane-2,4-dione
(6R)-8-oxo-7t-tritylamino-(6rH)-5-oxa-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid tert-butyl ester
(6R)-7t-((S)-2-hydroxy-2-phenyl-acetylamino)-8-oxo-(6rH)-5-oxa-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid tert-butyl ester