Iron Porphyrins and Iron Salens as Highly Enantioselective Catalysts for the Ring-Expansion Reaction of Epoxides to Tetrahydrofurans

Iron porphyrins have been found to be efficient catalysts for the ring-expansion reaction of epoxides with alkenes to give the corresponding tetrahydrofurans; very low loadings (down to 1 mol %) are sufficient to achieve high yields (up to 98%). Additionally, an iron(III) salen complex based on the axially chiral 1,1-binaphthalene backbone has been shown to catalyze the reaction with high enantioselectivity (<i>e.g</i>., 92% <i>ee</i> for calyxolane A).