(3S,4R)-benzyl 3-((R)-1-(tert-butyldimethylsilyloxy)ethyl)-azetidin-2-one-4-carboxylate

(3R,4R)-4-acetoxy-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-2-oxoazetidine

p-nitrobenzyl 2-diazo-3-(tert-butyldimethylsililoxy)-3-butenoate

(3S,4R)-3-[(R)-1'-(dimethyl-t-butylsilyloxy)ethyl]-4-oxoazetidin-2-carboxylic acid