allyl (8S,9R,10S)-10-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-5-methyl-11-oxo-1,5-diazatricyclo[7.2.0.03,8]undec-2-ene-2-carboxylate

allyl 1-benzyl-3-oxo-4-piperidinecarboxylate

allyl (8S,9R,10S)-5-(tert-butoxycarbonyl)-10-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-11-oxo-1,5-diazatricyclo[7.2.0.03,8]undec-2-ene-2-carboxylate

1-Benzyl-4-{(2S,3S)-1-(tert-butyl-dimethyl-silanyl)-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-3-oxo-piperidine-4-carboxylic acid allyl ester

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

(R)-4-{(2R,3S)-1-(tert-Butyl-dimethyl-silanyl)-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-3-oxo-piperidine-1-carboxylic acid tert-butyl ester

(R)-4-{(2R,3S)-1-Allyloxyoxalyl-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-3-oxo-piperidine-1-carboxylic acid tert-butyl ester

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

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