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

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

(3S,4R)-N-benzyl-3-((R)-1-((tert-butyldimethylsilyl)oxy)ethyl)-2-oxo-4-(prop-2-yn-1-yl)azetidine-1-carboselenoamide

(3S,4R)-3-((R)-1-((tert-butyldimethylsilyl)oxy)ethyl)-2-oxo-4-(prop-2-yn-1-yl)-N-(p-tolyl)azetidine-1-carboselenoamide

(3S,4R)-3-((R)-1-((tert-butyldimethylsilyl)oxy)ethyl)-N-(naphthalen-2-yl)-2-oxo-4-(prop-2-yn-1-yl)azetidine-1-carboselenoamide