Mn-Mediated Radical-Ionic Annulations of Chiral <i>N</i>‑Acylhydrazones

Sequencing a free radical addition and nucleophilic substitution enables [3 + 2] and [4 + 2] annulations of <i>N</i>-acylhydrazones to afford substituted pyrrolidines and piperidines. Photolysis of alkyl iodides in the presence of Mn₂(CO)₁₀ leads to chemoselective iodine atom abstraction and radical addition to <i>N</i>-acylhydrazones without affecting alkyl chloride functionality. Using radical precursors or acceptors bearing a suitably positioned alkyl chloride, the radical addition is followed by further bond construction enabled by radical–polar crossover. After the alkyl radical adds to the imine bond, the resulting <i>N</i>-nucleophile displaces the alkyl chloride leaving group via 5-<i>exo</i>-<i>tet</i> or 6-<i>exo</i>-<i>tet</i> cyclizations, furnishing either pyrrolidine or piperidine, respectively. When both 5-<i>exo-tet</i> and 6-<i>exo-tet</i> pathways are available, the 5-<i>exo-tet</i> cyclization is preferred. Isolation of the intermediate radical adduct, still bearing the alkyl chloride functionality, confirms the order of events in this radical–polar crossover annulation. A chiral oxazolidinone stereocontrol element in the <i>N</i>-acylhydrazones provides excellent stereocontrol in these reactions