| 研究課題/領域番号 |
26810017
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| 研究機関 | 東京大学 |
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研究代表者 |
ユー ウージン 東京大学, 理学(系)研究科(研究院), 助教 (70626077)
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| 研究期間 (年度) |
2014-04-01 – 2016-03-31
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| キーワード | single-electron transfer / C-H bond activation / bifunctional catalyst / photocatalyst / aerobic oxidation / visible light |
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| 研究実績の概要 |
The funded research is based on the use of SET processes in organic synthesis. In the first topic, we developed a new zinc antimonate salt as a unique bifunctional catalyst that possessed the ability to act as an aerobic oxidation catalyst to oxidize amines, and as a Lewis acid to activate the in-situ generated imine. This catalyst was shown to facilitate the allylation of N-aryl glycine ester derivatives under mild aerobic conditions. Furthermore, during our investigations into understanding the underlying role of antimonate anions as an aerobic oxidation catalyst, we discovered that free-radical initiators could be used to facilitate CDC reactions. Based on this knowledge, we developed a metal-free CDC reaction of tertiary amines in air. In our second topic, we investigated the use of visible light photoredox catalysis to mediate CDC reactions in air. We developed a new polymer-supported Ir-based photocatalyst that enabled the CDC reaction of tertiary amines. It was found that this active heterogeneous photocatalyst was quite robust and could be recovered several times without significant loss of catalytic activity.
While the major purpose of this funded research was based on the use of SET processes to activate organic substrates for synthesis, we considered the possibility of using SET processes to activate metal complexes. Based on this consideration, we demonstrated that copper catalysis and visible light photocatalysis can be productively merged to facilitate cross-coupling reactions of anilines and aryl boronic acids (Chan-Lam reaction) with challenging substrates.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
This funded research is progressing better than expected. Our stated goal was to develop SET processes that would enable challenging cross-coupling reactions of C-H bonds and this was achieved. Most of the projects stated in the original proposal, namely the development of a metal antimonate as a bifunctional catalyst and an immobilized visible light photoredox catalyst, were completed. Since these projects were completed before the anticipated timeline, we moved beyond the proposed research and into new and interesting direction in utilizing SET processes in organic synthesis.
For example, by trying to understand the nature of the antimonate anion as an aerobic oxidation catalyst, we were able to develop the ideal CDC reaction that occurs under metal-free conditions in air. This is important since we can avoid the use of toxic metals and dangerous peroxides as oxidants.
In addition, our proposed research originally considered the use of SET processes to activate organic compounds. However, after the completion of the visible light photoredox catalyzed CDC project, we considered the next step for these redox-active metal catalysts, which was to move away from activation of organic compounds by SET processes to activation of transition metals. This led us to develop a visible light-mediated C-N coupling reactions of anilines and aryl boronic acids that was superior to the originally reported catalytic system. We anticipate that the combination of photocatalysis with other metal catalyzed reactions will lead to new and exciting chemistry.
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| 今後の研究の推進方策 |
Although our original proposal discussed only the use of SET processes to activate amines for C-H functionalization reactions, based on our current discoveries, a new direction of the research will be pursued.
Cross-coupling reactions are one of the most widely utilized methods to form C-C and C-heteroatom bonds. We plan to merge visible light photoredox (SET) catalysis with transition metal catalysis to develop new cross-coupling reactions that occurs under mild conditions and with unique coupling partners. For the following fiscal year, we will focus on examining the productive merger between copper catalysis and photocatalysis for C-heteroatom bond formation processes. In our preliminary report, we demonstrated that anilines and aryl boronic acids could undergo the oxidative coupling reaction. We will further investigate the visible light-mediated Chan-Lam reactions with other types of heteroatom nucleophiles (amides, alcohols, thiols, etc) to improve upon known limitations (poor substrate scope, high copper loading). In addition, other classes of C-N coupling reactions, such as the coupling of amines with aryl halides (Ullmann-type) and reductive coupling of N-acyloxyphthalimides with aryl halides, will be investigated.
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