Remote Enantioselective Epoxidation Reactions Catalyzed by Chiral Iron Porphyrin Complexes with a Hydrogen-Bonding Site

Iron porphyrin complexes, which were linked via a paraphenylethynyl group to a chiral scaffold with a lactam binding site, were probed as catalysts in the enantioselective epoxidation of 4-(?-alkenyl)- quinolones. It was found that the 3-butenyl group in the substrate accounts for the highest enantioselectivity (up to 44% ee) and the absolute configuration of an oxirane product was elucidated by electron diffraction. A two-point hydrogen bond of the substrate to the catalyst is likely responsible for enantioface differentiation at a remote position. The study shows chirality transfer to be possible via four nonstereogenic carbon atoms between the binding site of the substrate and its reactive C=C double bond.