Diastereo‐ and Enantioselective Synthesis of Functionalized β‐Lactams from Oxiranecarbaldimines and Lithium Ester Enolates

The 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 (2 S ,3 S )‐ 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)