Photo-induced two-carbon ring expansion of N-alkenyl lactams and N-alkenyl/phenyl benzoazetinones

Abstract

Photo-induced ring expansion of N-alkenyl-γ-lactams is a unique transformation that enables the direct insertion of a two-carbon unit into the C–N bond of lactams. Historically, its synthetic potential has remained largely underdeveloped due to rare studies. In the present work, we have revisited this old and underevaluated reaction, which allows us to delineate its full chemical profile for the first time. More importantly, we proved that several other types of lactams, including N-alkenyl-β-lactams, N-alkenyl benzoazetinones and N-phenyl benzoazetinones, could also undergo similar photochemical transformations, thus notably enriching the toolbox of two-carbon ring-expansion reactions. To showcase the potential of the developed reactions, some of the resulting products have been transformed to skeletally diverse bioactive molecules.