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

Michel Kristin, Fröhlich Roland, Würthwein Ernst-Ulrich

Abstract

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 (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.