(3S,4S)-4-(1-methylallenyl)-3-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-2-azetidinone

(5R,6S)-6-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2-methyl-1-aza-bicyclo[3.2.0]hept-2-en-7-one

allyl (5S,6S,7R)-5-[(R)-1-hydroxyethyl]-4-oxo-9-thia-3-azatricyclo[5.4.0.03,6 ]undec-1-ene-2-carboxylate

allyl (5S,6S,7S)-5-[(R)-1-hydroxyethyl]-4-oxo-9-thia-3-azatricyclo[5.4.0.03,6 ]undec-1-ene-2-carboxylate

(3S,4R)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-but-2-ynyl-azetidin-2-one