2-bromo-3-methyl-crotonic acid
3-Methyl-2-methoxy-2-butenoic acid
7t-(N'-tert-butoxycarbonyl-hydrazinocarbonyl)-2,2-dimethyl-8-oxo-(6rH)-4-thia-1-aza-bicyclo[4.2.0]octane-3t-carboxylic acid benzyl ester
7t-(N'-tert-butoxycarbonyl-hydrazinocarbonyl)-2,2-dimethyl-8-oxo-(6rH)-4-thia-1-aza-bicyclo[4.2.0]octane-3c-carboxylic acid benzyl ester
7t-tert-butoxycarbonylamino-2,2-dimethyl-8-oxo-(6rH)-4-thia-1-aza-bicyclo[4.2.0]octane-3t-carboxylic acid benzyl ester