(3S,4R)-1-(tert-Butyl-dimethyl-silanyl)-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-chloro-azetidin-2-one

{(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-ylsulfanyl}-acetic acid methyl ester

4-[(2R,3S)-3-((R)-1-Hydroxy-ethyl)-4-oxo-azetidin-2-yl]-3-oxo-butyric acid benzyl ester

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

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