methyl 4-[[(1,1-dimethylethyl)diphenylsilyl]oxy]butanoate

methyl (1S,3R,5R,7R)-3-(tert-butyl)-7-chloro-6-oxo-7-(2-tert-butyldiphenylsilyloxy)ethyl-2-oxa-4-azabicyclo[3.2.0]heptane-4-carboxylate

tert-butyl (1S,3R,5S,7S)-3-(tert-butyl)-7-chloro-7-[2-(tert-butyldiphenylsilyloxy)ethyl]-2-oxa-6-oxo-4-azabicyclo[3.2.0]heptane-4-carboxylate