A new iodine-based catalyst for asymmetric synthesis

Professor Kazuaki Ishihara and colleagues at Nagoya University (Nagoya, Japan;www.nubio.nagoya-u.ac.jp/indexe.HTM) has discovered an efficient, chiral, salt-based hypervalent iodine catalyst that could replace toxic metal catalysts without generating the waste or explosion risks associated with hypervalent organo-iodine complexes. The researchers took the radical step of swapping iodine bonded to carbon for an iodite (IO2–) or hypoiodite (IO–) anion as the oxidant, which can be generated from iodide (I–) by simple oxidants, such as hydrogen peroxide. The team also coupled the (hypo)iodite with a chiral, quaternary-amine counter ion to solubilize the inorganic iodite in organic solvents and provide a chiral environment to control the geometry of the reaction. In the laboratory, the researchers performed an enantio-selective, oxidative cycloetherification of ketophenols to 2-acyl-2,3-dihydrobenzofuran derivatives — a key structure in several biologically active compounds — catalyzed by in-situ-generated chiral, quaternary-ammonium-(hypo)iodite salts, with hydrogen peroxide as an environmentally benign oxidant (only water and alcohol are generated as byproducts). After recrystallization, an optical purity…