(3S,4R)-3-((R)-1-(tert-butyldimethylsilyloxy)ethyl)-4-((E)-2,3-diiodoallyl)azetidin-2-one

(5R,6S)-6-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-1-aza-bicyclo[3.2.0]hept-3-en-7-one

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

(5R,6S)-3-Allyl-6-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-2-(4-methoxy-phenyl)-1-aza-bicyclo[3.2.0]hept-2-en-7-one

(2S,5R,6S)-3-[1-(4-Fluoro-benzenesulfonyl)-meth-(Z)-ylidene]-6-((R)-1-hydroxy-ethyl)-7-oxo-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid 4-nitro-benzyl ester