Synthesis of 4-aryl-azetidinones via intramolecular alkylation of nucleophilic arenes using acyliminium cations

The acyliminium cations derived from 4-vinyloxy- or 4-acyloxy-azetidin-2-ones in the presence of Lewis acids can alkylate nucleophilic arenes bound to the β-lactam nitrogen atom through methyloxy, or methylthio tethers. The reactions smoothly proceed to afford the corresponding 3-oxa- or 3-thia-4,5-benzocephams in a good yield. The sulfur atom can be easily removed by Raney nickel reduction to provide the title compounds.