| 摘要 |
Compounds having the formula <IMAGE> and pharmaceutically acceptable salts thereof, wherein R3 and R4 are the same or different and each is hydrogen or alkyl or R3 and R4 taken together with the nitrogen atoms to which they are attached form a 1,2-diazacyclobutane, 1,2-diazacyclopentane, 1,2-diazacyclohexane, or 1,2-diazacycloheptane ring and Y, and Y2 are either hydrogen or hydroxy but are not the same; are useful chemical intermediates for the preparation of beta -lactam antibiotics.
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