Intramolecular Cyclopropanation of Active Methylene Derivatives Based on FeCl₂ or FeCl₃‐Promoted Radical‐Polar Crossover Reactions

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Radical‐polar crossover reactions were studied for the intramolecular cyclopropanation of active methylene derivatives. In the presence of FeCl 3 as a stoichiometric oxidant and K 2 HPO 4 as a base, the dehydrogenative cyclopropanation of active methylenes proceeded through the FeCl 3 ‐promoted oxidative radical cyclization followed by the ionic cyclization to give the bicyclic cyclopropanes. The use of α‐chloro‐active methylenes leads the subcatalytic cyclopropanation involving two redox pathways. In the presence of K 2 HPO 4 , the redox cyclopropanation proceeded by using FeCl 2 (20 mol%) in combination with ligand (20 mol%).