Synthesis of α-Methylene-β-Lactams via PPh3-Catalyzed Umpolung Cyclization of Propiolamides

We report herein a facile synthesis of α-methylene-β-lactams. Thus, under the catalysis of triphenylphosphine, a number of 2-propiolamidoacetates or α-propiolamido ketones in refluxing ethanol underwent umpolung cyclization to afford the corresponding 4-substituted 3-methyleneazetidin-2-ones in high yields.