3,3-diethoxy-4-ethyl-1-(4-nitro-benzenesulfonyl)-azetidin-2-one
{1-[Diethoxy-((S)-1-hydroxymethyl-2-phenyl-ethylcarbamoyl)-methyl]-propyl}-carbamic acid allyl ester
{1-[diethoxy-(4-methoxy-benzylcarbamoyl)-methyl]-propyl}-carbamic acid allyl ester
3,3-diethoxy-4-ethyl-1-(toluene-4-sulfonyl)-azetidin-2-one