Intramolecular Cyclopropanation of Active Methylene Derivatives Based on FeCl or FeCl-Promoted Radical-Polar Crossover Reactions.

Radical-polar crossover reactions were studied for the intramolecular cyclopropanation of active methylene derivatives. In the presence of FeCl as a stoichiometric oxidant and KHPO as a base, the dehydrogenative cyclopropanation of active methylenes proceeded through the FeCl-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 KHPO, the redox cyclopropanation proceeded by using FeCl (20 mol%) in combination with ligand (20 mol%).