(5R,6S)-3-Ethylsulfanyl-7-oxo-6-[(R)-1-(2,2,2-trichloro-ethoxycarbonyloxy)-ethyl]-4-thia-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid allyl ester

{(2S,3R)-2-Ethylsulfanylthiocarbonylsulfanyl-4-oxo-3-[(S)-1-(2,2,2-trichloro-ethoxycarbonyloxy)-ethyl]-azetidin-1-yl}-acetic acid allyl ester

Carbonic acid (S)-1-[(2S,3R)-2-ethylsulfanylthiocarbonylsulfanyl-4-oxo-1-((1R,5R)-2-oxo-3-oxa-bicyclo[3.1.0]hex-1-yl)-azetidin-3-yl]-ethyl ester 2,2,2-trichloro-ethyl ester

Carbonic acid (R)-1-[(2R,3S)-2-ethylsulfanylthiocarbonylsulfanyl-4-oxo-1-((1R,5R)-2-oxo-3-oxa-bicyclo[3.1.0]hex-1-yl)-azetidin-3-yl]-ethyl ester 2,2,2-trichloro-ethyl ester