Direct allylic C-H alkylation of enol silyl ethers enabled by photoredox-Bronsted base hybrid catalysis
Direct allylic C-H alkylation of enol silyl ethers enabled by photoredox-Bronsted base hybrid catalysis
复制标题
DOI：
10.1038/s41467-019-10641-y
复制
发表时间：
2019-06-20
影响因子：
16.6
通讯作者：
Ooi, Takashi
中科院分区：
文献类型：
--
作者：
Ohmatsu, Kohsuke;Nakashima, Tsubasa;Ooi, Takashi
改变反应中间体反应路径的策略对于使有机合成多样化具有重要意义。烯醇硅基醚是一种用途广泛的烯醇硅酸酯的等价物，它们经过单电子氧化生成自由基阳离子，这些阳离子通过消除硅基自发地形成亲电的α-羰基自由基。在这里，我们证明，通过仔细研究自由基阳离子作为强C-H酸的性质，可以识别出由Ir基光敏剂和2，4，6-Coldine组成的催化剂体系，该催化体系用于从烯醇硅醚在光照射下通过单电子氧化-去质子化序列生成亲核烯丙基自由基，而不需要自由基阳离子中间体的脱硅化。生成的烯丙基参与缺电子烯烃的加成反应，建立了烯醇硅醚的选择性烯丙基C-H烷基化反应。这一策略具有广泛的适用性，烷基化烯醇型硅烷基醚可以利用其共同的极性反应性转化为高度官能化的羰基化合物。
Strategies for altering the reaction pathway of reactive intermediates are of significant importance in diversifying organic synthesis. Enol silyl ethers, versatile enolate equivalents, are known to undergo one-electron oxidation to generate the radical cations that spontaneously form electrophilic alpha-carbonyl radicals via elimination of the silyl groups. Here, we demonstrate that close scrutiny of the property of the radical cations as strong C-H acids enables the identification of a catalyst system consisting of an iridium-based photosensitizer and 2,4,6-collidine for the generation of nucleophilic allylic radicals from enol silyl ethers through one-electron oxidation-deprotonation sequence under light irradiation without the desilylation of the radical cation intermediates. The resultant allylic radicals engage in the addition to electron-deficient olefins, establishing the selective allylic C-H alkylation of enol silyl ethers. This strategy is broadly applicable, and the alkylated enol silyl ethers can be transformed into highly functionalized carbonyl compounds by exploiting their common polar reactivity.