2-((2R,3S)-3-Ethyl-4-oxo-azetidin-2-ylsulfanyl)-3-oxo-succinic acid 4-benzyl ester 1-ethyl ester
chlorophosphoric acid diphenyl ester
2-[(2R,3S)-1-(tert-Butyl-dimethyl-silanyl)-3-ethyl-4-oxo-azetidin-2-ylsulfanyl]-3-oxo-succinic acid 4-benzyl ester 1-ethyl ester
4-acetoxy-3-ethyl-azetidin-2-one
dibenzyl oxalate