Monodentate Halogen Bond Activation of Aziridines in Formal [3+2] Cycloadditions

The ring opening of aziridines to produce various N-heterocycles traditionally requires strong Lewis acids or transition metal catalysts, with non-covalent organocatalytic approaches remaining largely unexplored. Herein, we demonstrate that N-heterocyclic iodonium salts can effectively catalyze [3+2] cycloadditions of aziridines through a monodentate halogen bond (XB) activation. Using 1-5 mol% of the iodolium catalyst, a wide range of aziridines undergo an efficient cycloaddition with a variety of dipolarophiles (carbonyls, alkynes, and alkenes) to furnish oxazolidines, pyrrolines, and pyrrolidines. DFT calculations revealed a previously underexplored N-activation mode, with detailed non-covalent interaction analysis showing that the N-heterocyclic iodonium salt's exceptional performance stems from combined I-N and I-π interactions.