Abstract
AbstractThe addition of nucleophiles like lithium ester enolates 6 to oxiranecarbaldimines 1 leads to new oxiranyl‐functionalised β‐lactams 7 in excellent enantio‐ and diastereoselectivity. A simple one‐pot procedure affords β‐lactams (azetidin‐2‐ones) with three or four neighbouring stereogenic centres and unlike preference. Products resulting from oxirane ring‐opening reactions were not observed. An enantiomerically enriched example (2S,3S)‐1g gave the corresponding β‐lactam (S,S,R)‐7f in excellent enantiomeric excess. According to quantum chemical calculations the observed diastereoselectivity is the result of a diastereofacial differentiation of the two faces of the iminic double bond in the transition state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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