Readily available 4-formyloxyazetidinone was enantioselectively transformed into 3,4-benzo-2-hydroxy-5-oxacephams and 4-phenyloxyazetidinones upon treatment with 0.1 equiv of the cinchona alkaloid in toluene via intermolecular nucleophilic trapping of N-acyliminium intermediate by the hydroxyl moiety of phenols or o-hydroxybenzaldehydes. Additionally, the absolute configuration of title compounds was
the azetidin-2-one ring. The most common strategy for the synthesis of 4-alkoxyazetidinons involves intramolecular nucleophilic substitution at C4 that leads to ring closure. Such a displacement proceeds via the flat intermediate that suppossedly has the structure of a mezomeric acyl ammonium cation. We herein report a novel and enantioselective, chiral Lewis acid mediated cyclization that affords the
4-acyloxy-azetidinones in the presence of Lewis acids can be used to alkylate nucleophilic arenes in both the inter- and intramolecular processes. The former reactions were successfully carried out with p-dimethoxy-benzene in moderate yield, whereas the latter reactions can be done with a variety of nucleophilic arenes in a good yield.