C-H，C-Si，Si-Si，Si-H通过可见光诱导的阳离子自由基裂解活化

Among the visible-light-mediated photoredox catalysis, radical cation species effectively generated through reductive quenching of the excited photocatalyst via a single electron transfer (SET) process, have frequently been involved to achieve many important transformations. Fragmentation is an appealing reaction pathway for radical cations, which can introduce radical intermediates in a convenient manner. However, useful synthetic transformations based on fragmentation of radical cations generated by photo-induced SET are scarce. The reported successful transformations via radical cation fragmentation mechanism are almost conducted under UV light, and no example has been disclosed through the visible-light promoted photoredox catalysis. The major challenge is (i) to find a photo-catalyst that is capable of oxidizing a wide range of substrates, (ii) can minimize unproductive ion-pair induced back electron transfer or cation-anion interaction, and (iii) will not interact with the generated allylic/benzylic radical..The proposed research thus aims to develop a visible-light promoted photoredox catalysed radical cation fragmentation to smoothly deliver carbon- or silicon-based radicals through C-H, C-Si, Si-Si, or Si-H activation. These generated carbon- and silicon-based radicals are versatile intermediates that behave as organometallic nucleophile equivalents and can be applied to a variety reaction pathways, such as nucleophilic addition to Michael acceptors, arylation with electron deficient arenes, and cross coupling with alkyl/aryl halogens with the merging of transition-metal catalysis, to prepare a wide range of value-added chemicals. A centrepiece of the proposed research will rely on the unique advantages provided by an organo-acridinium photo-oxidant catalyst. Success on the proposed study will provide a convenient and green protocol to use C-H, C-Si, Si-Si, or Si-H bonds as latent nucleophilic handles. Very promising preliminary results on methodology development along this line have been obtained. In particular, a metal-free direct alkylation of allylic/benzylic C-H bonds has been achieved in an atom-, redox-, and catalyst-economical manner. This fully support our hypothesis that such an endeavour will likely be successful. Our newly invented SFMT reactor will be applied to improve the reaction efficiency during reaction discovery owing to the enhanced the photo irradiation with micro-flow tubings according to the Beer-Lambert Law. A successful reaction discovered in SFMT reactor can be seamlessly transformed to the continuous-flow system for scale-up production.

在可见光激发的氧化还原催化中，经自由基阳离子的分裂解离是很诱人的引入自由基中间体的方式。然而，基于由光诱导SET产生的自由基阳离子断裂的合成方法非常罕见。已报道成功通过自由基阳离子断裂机理的转化绝大多数是在紫外光下进行，目前还没有通过可见光促进催化的报道。其主要的挑战是 1）找到适用于宽泛底物的光催化剂，2）不会导致电子回流，3）激发态光催化剂不会与产生的烯丙基/苄基自由基反应。因此，此研究旨在开发可见光促进的光致氧化还原催化的自由基阳离子断裂形成碳或硅的自由基，实现C-H，C-Si，Si-Si或Si-H活化。此研究将依赖于有机acridinium光氧化催化剂提供的独特优点。所提议研究的成功将给出使用C-H，C-Si，Si-Si或Si-H键作为潜在亲核试剂的绿色方案。基于根据比尔-朗伯定律微流管的光辐照会增强，我们新发明的“停止流动”微管反应器将用于提高研发反应的效率。

可见光诱导的惰性C-H和Si-H键的解离是一类引入碳和硅自由基中间体的高效方式，然而，已报道的例子有限。本项目旨在开发可见光诱导的C-H和Si-H键的活化的方法学，实现含惰性C-H和Si-H键的廉价易得分子的高附加值转化。经过本项目课题组三年的努力，基于惰性C-H键的活化，成功实现了可见光协同路易酸催化惰性苄基C(sp3)-H键与缺电子烯烃的加成反应，可见光协同氢原子转移催化C-H键与烯烃的双官能团化反应，可见光协同钴催化C(sp2)-H键与烯烃的交叉偶联，可见光协同路易斯酸催化C(sp2)-H键的不对称加成反应；基于惰性Si-H键的活化，成功实现了可见光协同氢原子转移催化Si-H键与烯烃的硅氢化反应和双官能团化反应，可见光协同氢原子转移催化硅烷Si-H键的氘代反应和氯代反应。本项目发展了7类绿色的可见光诱导的C-H和Si-H键的活化的方法学，实现了一系列高附加值分子的高效合成，首次报道了可见光诱导的 Si-H键的官能团化方法学，推动了Si-H 和C-H键的官能团化领域的发展，在国际顶尖期刊发表7篇高水平论文，其平均IF>10，其研究成果被多个专业期刊和网站所评述，如： Synfacts，Org. Process Res. Dev.，X-Mol，WeeChem，Organic Chemistry Portal，一篇被选为 Chemical Science封面