Single-Electron-Transfer Strategy for Reductive Radical Cyclization: Fe(CO)₅ and Phenanthroline System

An electron-transfer strategy using low-valent iron pentacarbonyl [Fe(CO)₅] to generate radical species from alkyl iodides was achieved. A range of pyrrolidines, tetrahydrofurans, and carbocycles were synthesized via 5-exo cyclization reactions of alkyl radical intermediates generated by electron transfer from a system involving Fe(CO)₅, 1,10-phenanthroline, and diisopropylamine. Moreover, tandem addition reactions with Michael acceptors were also explored. Photophysical and electrochemical studies support a mechanism that involves electron transfer from the low-valent Fe reductant to alkyl iodide.