(1S,2R,5R)-6-(2,4-Dimethoxy-benzyl)-4-hydroxy-2,4-dimethyl-3-oxa-6-aza-bicyclo[3.2.0]heptan-7-one

(R*,R*)-N-bis(carboethoxy)methyl-N-tert-butoxycarbonylmethyl-2-bromo-3-acetoxybutylamide

<3α(S*),4α>-1-tert-butoxycarbonylmethyl-3-(1-acetoxyethyl)-4-ethoxycarbonyl-2-azetidinone-4-carboxylic acid