Monocyclic Azetidines via a Visible-Light-Mediated Aza Paternò-Büchi Reaction of Ketone-Derived Sulfonylimines

The recent rise in popularity of azetidines in pharmaceutical chemistry has inspired the development of visible-light-mediated aza Paternò-Büchi reactions as direct transformations to form these desirable products. Despite these advancements, successful reports of accessing monocyclic azetidines from acyclic imines remain scarce. Here, we report a visible-light-mediated aza Paternò-Büchi reaction of acyclic ketone-derived sulfonylimines, which are previously unexplored substrates in this transformation, with activated alkenes (i.e., styrenes and dienes) to form 2,2-disubstituted monocyclic azetidines that can be further modified to reveal free N-H azetidines. Computational and experimental mechanistic studies reveal that in contrast to aldehyde-derived oximes, the use of ketone-derived sulfonylimines enables tuning of the reaction mechanism to favor initial formation of the C-N rather than C-C bond, thus enabling access to 2,2-disubstituted monocyclic azetidine scaffolds.