p-nitrobenzyl 3,5-hexadienoate

(4-Oxo-azetidin-2-yl)-acetic acid benzhydryl ester

2-Diazo-4-[1-(2,4-dimethoxy-benzyl)-4-oxo-azetidin-2-yl]-3-oxo-butyric acid 4-nitro-benzyl ester

p-nitrobenzyl 4-(2-azetidinon-4-yl)-3-butenoate

p-nitrobenzyl 4-(N-chlorosulfonyl-2-azetidinon-4-yl)-3-butenoate