4-nitrobenzyl 2-((3S,4S)-3-((R)-1-((tert-butyldimethylsilyl)oxy)ethyl)-2-oxo-4-((R)-1-oxo-1-(((R)-5-oxopyrrolidin-3-yl)thio)propan-2-yl)azetidin-1-yl)-2-(triethoxy-l5-phosphaneylidene)acetate

4-nitrobenzyl 2-((3S,4S)-3-((R)-1-((tert-butyldimethylsilyl)oxy)ethyl)-2-oxo-4-((R)-1-oxo-1-(((R)-5-oxopyrrolidin-3-yl)thio)propan-2-yl)azetidin-1-yl)-2-(diethoxy(ethyl)-l5-phosphaneylidene)acetate

(3S,4S)-3-[(R)-1-[[(R)-2-oxopyrrolidin-4-ylthio]carbonyl]ethyl]-3-[(R)-1-(trimethylsilyloxy)ethyl]-2-azetidinone

(3S,4S)-3-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-1-[[(p-nitrobenzyl)oxy]oxalyl]-4-[(R)-1-[[(R)-2-oxopyrrolidin-4-ylthio]carbonyl]ethyl]-2-azetidinone