title: High-turnover hypoiodite catalysis for asymmetric synthesis of tocopherols.
abstract: The diverse biological activities of tocopherols and their analogs have inspired considerable interest in the development of routes for their efficient asymmetric synthesis. Here, we report that chiral ammonium hypoiodite salts catalyze highly chemo- and enantioselective oxidative cyclization of γ-(2-hydroxyphenyl)ketones to 2-acyl chromans bearing a quaternary stereocenter, which serve as productive synthetic intermediates for tocopherols. Raman spectroscopic analysis of a solution of tetrabutylammonium iodide and tert-butyl hydroperoxide revealed the in situ generation of the hypoiodite salt as an unstable catalytic active species and triiodide salt as a stable inert species. A high-performance catalytic oxidation system (turnover number of ~200) has been achieved through reversible equilibration between hypoiodite and triiodide in the presence of potassium carbonate base. We anticipate that these findings will open further prospects for the development of high-turnover redox organocatalysis.
authors.affiliation: Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan.
authors.forename: Muhammet
authors.initials: M
authors.lastname: Uyanik
authors.affiliation: Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Hayashi
authors.affiliation: Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan. Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Furo-cho, Chikusa, Nagoya 464-8603, Japan. ishihara@cc.nagoya-u.ac.jp.
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Ishihara
mesh_terms: D002384:Catalysis; D020134:Catalytic Domain; D002839:Chromans / Q000737:chemistry*; D003500:Cyclization; D017613:Iodine Compounds / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D010084:Oxidation-Reduction; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D024505:Tocopherols / Q000138:chemical synthesis* / Q000737:chemistry; D020122:tert-Butylhydroperoxide / Q000737:chemistry
chemical_list: D002839:Chromans; D017613:Iodine Compounds; D007659:Ketones; D000644:Quaternary Ammonium Compounds; C081961:hypoiodous acid; D020122:tert-Butylhydroperoxide; C009405:tetrabutylammonium; D024505:Tocopherols