(R)-4-3'-benzyloxycarbonyl-3'-diazo-2'-oxopropyl-2-azetidinone

p-nitrobenzyl (3R,5R)-1-carba-2-oxopenam-3-carboxylate

(S)-N-benzyl-4-carboxymethyl-2-azetidinone

(S)-(isobutyl carbonic) (S)-2-(4-oxoazetidin-2-yl)acetic anhydride

(R)-4-3'-diphenylmethyloxycarbonyl-3'-p-nitrobenzyloxycarbonyl-2'-oxopropyl-2-azetidinone