2-Allyl-2-{(2S,3S)-1-allyloxyoxalyl-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-malonic acid diethyl ester

{(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-thioacetic acid S-((S)-1-{1-[(Z)-4-nitro-benzyloxycarbonylimino]-ethyl}-pyrrolidin-3-yl) ester

(2S,2aS,2bR,5aR,6S)-2-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2b-methyl-1,4-dioxo-5a-phenylsulfanyl-octahydro-3-oxa-6a-aza-cyclobuta[a]pentalene-6-carboxylic acid benzyl ester

(2S,2aS,2bR,5aR,6S)-5a-Benzenesulfonyl-2-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-2b-methyl-1-oxo-octahydro-3-oxa-6a-aza-cyclobuta[a]pentalene-6-carboxylic acid benzyl ester

(4R,5R,6S)-6-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-3-(diphenoxy-phosphoryloxy)-4-methyl-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid allyl ester