Metalloradical Activation of Iodonium Ylides for Catalytic Radical Cyclization via Fe(III)-Based Metalloradical...

Transition metal-catalyzed olefin cyclization via metalloradical catalysis (MRC) is a highly versatile strategy for synthesizing functionalized cyclopropanes and furans. However, mostly diazo compounds have been used as metalloradicophiles for the formation of α-metalloalkyl radical complexes. These compounds suffer from limitations in their use; their explosive or hazardous nature makes them challenging to work with. The most employed catalysts in MRC, Co-(II) porphyrin complexes, are stable in their solid forms in open air, but remain susceptible to oxidation in solution and require inert reaction conditions during catalysis. In this work, we have explored cyclic iodonium ylides as surrogate metalloradicophiles using air-stable Fe-(III)-porphyrin complex, Fe^III(TPP)-Cl, as a metalloradical catalyst for olefin spiro/cyclization to afford cyclopropanes, dihydrofurans, and furans. Combined experimental and computational mechanistic studies reveal that the present catalytic system effectively suppresses the metallacyclic N-enolate off-cycle pathway, typically associated with Fe-(III)-porphyrin and cyclic iodonium ylides. Electronic structure analyses further establish that the catalytic transformation proceeds via a stepwise radical pathway rather than a concerted ionic mechanism, suggesting Fe-(III) as the active catalyst and not the in situ generated Fe-(II) species.