thoxycarbonyl)methyl]-2-bromo-3-hydroxybutyramide (5) with DBU yielded the bicyclic β-actam 13 by a direct cyclization, and its diastereoisomer 14 and the γ-lactam 15 via the trans-epoxide 6. The same treatment of (2S,3R)-isomer (11) gave the direct cyclization product 14 in 93% yield. On the other hand, reaction of 5 and 11 with sodium hydride afforded the 2-azetidinone derivatives (mainly 14 (23%)