(R)-4-{(2R,3S)-1-(tert-Butyl-dimethyl-silanyl)-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-3-oxo-piperidine-1-carboxylic acid tert-butyl ester

allyl (8S,9R,10S)-5-allyloxycarbonyl-10-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-11-oxo-1,5-diazatricyclo[7.2.0.03,8]undec-2-ene-2-carboxylate

allyl (8S,9R,10S)-5-[2-[(allyloxycarbonyl-N-methyl)amino]acetyl]-10-[(R)-1-hydroxyethyl]-11-oxo-1,5-diazatricyclo[7.2.0.03,8]undec-2-ene-2-carboxylate

allyl (8S,9R,10S)-5-(tert-butoxycarbonyl)-10-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-11-oxo-1,5-diazatricyclo[7.2.0.03,8]undec-2-ene-2-carboxylate

allyl (8S,9R,10S)-5-[2-(allyloxycarbonylamino)acetyl]-10-[(R)-1-hydroxyethyl]-11-oxo-1,5-diazatricyclo[7.2.0.03,8]undec-2-ene-2-carboxylate