p-nitrobenzyl 2-<(3S,4R)-3-<(R)-1-(t-butyldimethylsilyloxy)ethyl>-4-<4-(p-nitrobenzyloxycarbonylamino)-2-oxobutyl>-2-oxo-1-azetidinyl>-2-triphenylphosphoranylideneacetate

1-{(2S,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-2-oxo-cyclohex-3-enecarboxylic acid allyl ester

(3S,4R)-4-(5-benzyloxypent-3-ynyl)-3-[(R)-1-tert-butyldimethylsilyloxyethyl]-2-azetidinone

(3S,4R)-4-[1-Buten-3(S)-yl]-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-2-azetidinone