trans-3-ethyl-4-phenylthioazetidin-2-one
p-nitrobenzyl 3-<<2-(tert-butyldimethylsilyloxy)ethyl>thio>-6-ethyl-7-oxo-4-thia-1-azabicyclo-<3.2.0>hept-2-ene-2-carboxylate
p-nitrobenzyl 2-<4-<<<<2-(tert-butyldimethylsilyloxy)ethyl>thio>thiocarbonyl>thio>-3-ethyl-2-oxo-1-azetidinyl>-2-hyxdroxyacetate
p-nitrobenzyl 2-<4-<<<<2-(tert-butyldimethylsilyloxy)ethyl>thio>thiocarbonyl>thio>-3-ethyl-2-oxo-1-azetidinyl>-2-chloroacetate
p-nitrobenzyl 2-<4-<<<<2-(tert-butyldimethylsilyloxy)ethyl>thio>thiocarbonyl>thio>-3-ethyl-2-oxo-1-azetidinyl>-2-(triphenylphosphoranylidene)acetate