BASE-INDUCED CYCLIZATION OF (2<i>R</i>,3<i>R</i>)- AND (2<i>S</i>,3<i>R</i>)-<i>N</i>-2,4-DIMETHOXYBENZYL-<i>N</i>-BIS(ETHOXYCARBONYL)METHYL-2-BROMO-3-HYDROXYBUTYLAMIDE
Reaction of (2R,3R)-N-2,4-dimethoxybenzyl-N-bis(ethoxycarbonyl)methyl-2-bromo-3-hydroxybutylamide (6) with DBU yielded bicyclic β-lactam 7 by a direct cyclization, and its diastereomer 8 and unexpected γ-lactam 9 by another non-direct cyclization. Also (2S,3R)-isomer 19 gave 8 as a sole product. On the other hand, reactions of 6 and 19 with NaH advanced to afford azetidin-2-one derivatives via the
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%)