Intramolecular Cyclopropanation of Active Methylene Derivatives Based on FeCl 2 or FeCl 3 -Promoted Radical-Polar Crossover Reactions.

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%).