cis-3-Ethyl-4-(methoxycarbonyl)-1-(4-methoxyphenyl)azetidin-2-one

cis-1-p-anisyl-3-ethyl-4-carboxy-2-azetidinone

(3S*,4R*)-N-(tert-butyldimethylsilyl)-3-ethyl-4-(phenylthio)azetidin-2-one

(2R,3R)-3-ethyl-1-(4-methoxyphenyl)-4-oxoazetidine-2-carboxylic acid