(E)-4-{(2R,3S)-1-(tert-Butyl-dimethyl-silanyl)-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-but-2-enal

(E)-4-[(2R,3S)-3-((R)-1-Hydroxy-ethyl)-4-oxo-azetidin-2-yl]-but-2-enoic acid methyl ester

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