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  • High-turnover hypoiodite catalysis for asymmetric synthesis of tocopherols.

High-turnover hypoiodite catalysis for asymmetric synthesis of tocopherols.

Science (New York, N.Y.) (2014-07-19)
Muhammet Uyanik, Hiroki Hayashi, Kazuaki Ishihara
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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Tetrabutylammonium cyanide, technical, ≥80%
Sigma-Aldrich
Tocopherols, mixed, Low-α type, FCC, FG
Sigma-Aldrich
Tetrabutylammonium perchlorate, ≥95.0% (T)
Sigma-Aldrich
Tetrabutylammonium hydroxide solution, technical, ~40% in H2O (~1.5 M)
Supelco
Tetrabutylammonium hydroxide solution, ~40% in water, suitable for ion chromatography
Sigma-Aldrich
Tetrabutylammonium hydroxide solution, 53.5-56.5% in H2O
Sigma-Aldrich
Tetrabutylammonium hydrogensulfate, 97%
Sigma-Aldrich
Tetrabutylammonium hydroxide solution, 1.0 M in methanol
Sigma-Aldrich
tert-Butyl hydroperoxide solution, 5.0-6.0 M in decane
Sigma-Aldrich
tert-Butyl hydroperoxide solution, 5.0-6.0 M in nonane
Sigma-Aldrich
tert-Butyl hydroperoxide solution, 70 wt. % in H2O
Sigma-Aldrich
Tetrabutylammonium cyanide, 95%
Sigma-Aldrich
Tetrabutylammonium phosphate monobasic solution, 1.0 M in H2O
Supelco
Tetrabutylammonium perchlorate, for electrochemical analysis, ≥99.0%
Sigma-Aldrich
Tetrabutylammonium hydroxide solution, 40 wt. % in H2O
Sigma-Aldrich
Tetrabutylammonium hydrogensulfate, anhydrous, free-flowing, Redi-Dri, 97%
Sigma-Aldrich
Tetrabutylammonium azide
Sigma-Aldrich
Tetrabutylammonium iodide, ≥99.0% (AT)
Sigma-Aldrich
Tetrabutylammonium bromide solution, 50 wt. % in H2O
Supelco
Tetrabutylammonium bisulfate solution, suitable for ion pair chromatography, LiChropur, concentrate, ampule
Sigma-Aldrich
Tetrabutylammonium fluoride solution, 75 wt. % in H2O
Sigma-Aldrich
Tetrabutylammonium nitrate, 97%
Sigma-Aldrich
Tetrabutylammonium bisulfate, puriss., ≥99.0% (T)
Supelco
Tetrabutylammonium chloride, suitable for ion pair chromatography, LiChropur, ≥99.0%
Supelco
Tetrabutylammonium bisulfate, suitable for ion pair chromatography, LiChropur, ≥99.0%
Supelco
Tetrabutylammonium bromide, suitable for ion pair chromatography, LiChropur, ≥99.0%
Sigma-Aldrich
Tetrabutylammonium phosphate monobasic, puriss., 99% (T)
Sigma-Aldrich
Tetrabutylammonium iodide, reagent grade, 98%
Sigma-Aldrich
Trimethylhydroquinone, 97%
Sigma-Aldrich
Tetrabutylammonium bromide, ACS reagent, ≥98.0%