Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan.
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.
Science. 2014 Jul 18;345(6194):291-4. doi: 10.1126/science.1254976.
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.
生育酚及其类似物的多种生物活性激发了人们对其高效不对称合成途径的极大兴趣。在这里，我们报告手性季铵次碘酸盐盐可以催化γ-（2-羟基苯基）酮的高化学选择性和对映选择性氧化环化，得到带有季立体中心的 2-酰基色满，它们可作为生育酚的有效合成中间体。四丁基碘化铵和叔丁基过氧化氢溶液的拉曼光谱分析表明，次碘酸盐盐作为不稳定的催化活性物种和三碘化物盐作为稳定的惰性物种原位生成。在碳酸钾碱的存在下，通过次碘酸盐和三碘化物之间的可逆平衡，实现了高活性催化氧化体系（周转率约为 200）。我们预计这些发现将为高周转率氧化还原有机催化的发展开辟进一步的前景。
