Photoinduced Pd-Catalyzed Carbonylative Formal [2 + 2] Cycloaddition of Alkylarenes and Imines

A photoinduced palladium-catalyzed carbonylative formal [2 + 2] cycloaddition of toluene derivatives and imines provides a direct access to β-lactams under mild conditions (35 °C, 455 nm LED, 2 bar CO) with up to 99% yields. This three-component reaction accommodates both aldimines and ketimines as well as diverse aryl substrates, including ethylbenzene derivatives. Mechanistic studies reveal a sequential process consisting of C-H bond activation, carbonylation, and in situ ketene formation. This atom-economical protocol offers a valuable synthetic route to pharmaceutically important β-lactam scaffolds directly from readily available starting materials.