光催化偶联—加氧氧化串联反应构建环状化合物的研究

发布时间：2018-05-17 08:05

本文选题：光催化 + 二氧化钛　；参考：《山东大学》2017年博士论文

【摘要】：太阳光和氧气是绿色无污染且取之不尽的宝贵资源,以太阳光为光源、氧气为氧化剂,高选择性的实现具有挑战性的化学反应,是科学家们不懈的追求。然而在有氧条件下,光催化体系中的活泼自由基可能会优先进一步失去电子或加氧氧化,从而导致C-C断裂的降解反应发生和偶联反应的失败。利用光催化实现高选择性的偶联氧化反应,除了要考虑催化剂的结构、底物的氧化还原电位以及溶剂等因素,还必须考虑光催化剂和底物的作用模式以及底物的反应动力学。在本博士论文中,我们构建了偶联—加氧氧化串联反应的光催化体系,通过动力学控制合理地调控偶联反应与加氧氧化反应的优先度,选择性地使偶联反应先于加氧氧化发生,从而避免了导致C-C键断裂的过度氧化等副反应的发生,实现了一系列高效的环化—氧化反应,从简单有机小分子底物出发,一步合成了四氢萘酮类木质素骨架、环过氧化合物、VA唑醛、吲哚醛等有机化合物。论文分为以下几个部分:第一章,首先简单介绍了光能的吸收和转化,光催化的基本概念和发展历程,光催化剂的分类、性质及原理;然后,详细综述了异相半导体光催化剂(如二氧化钛)和均相分子型光催化剂在光照条件下催化的各类有机反应;在此基础上,对各种光催化体系的优势和缺点做了总结和展望;最后对本博士论文的立题意义进行了阐述。第二章,以二氧化钛为异相光催化剂、O_2作为氧化剂,在不需要添加剂和电子牺牲体的条件下,成功实现了烯烃的光催化环化—氧化反应,合成了一系列四氢萘酮类化合物。该类化合物是天然产物木酚素的重要骨架结构。原料的[2+2]环加成产物,即1,2—二取代环丁烷,是该反应的稳定中间体,结构数据表明其全部为反式构型。太阳光光催化该反应取得了很好的产率。对催化剂结构效应、溶剂效应、反应动力学和光催化机理做了详细研究。机理研究表明:该反应涉及烯烃对自由基阳离子亲核进攻和加氧氧化两步反应;如果生成的自由基阳离子具有足够的化学稳定性以适合另一烯烃分子对其亲核进攻,选择性地使偶联反应优先于加氧氧化发生,就会有效的避免导致C-C键断裂的过度氧化的发生,从而提高环化反应的效率。第三章,为了克服1,2—二取代烯烃的空间位阻效应,实现该类化合物在二氧化钛光催化中高效转化为四氢萘酮产物,本章中我们采用了两种策略:(1)考察了 TiO_2光催化的分子内的环化—氧化反应,利用分子内反应的动力学优势,克服烯烃β-位取代基的空间位阻效应;(2)先合成1,2—二取代烯烃的[2+2]环化产物,然后以此为原料在二氧化钛光催化条件下进行扩环—氧化反应。基于此,以很高的非对映选择性合成了一系列四氢萘酮产物,并实现了从基础原料出发的天然木酚素(-)-8'-epi-aristoligone的两步全合成。第四章,为了进一步拓展太阳光光催化环化—氧化串联反应在有机合成中的应用,我们选择了既具有可见光活性又具有π路易斯酸性的碘单质代替二氧化钛,催化炔丙基酰胺的环化—氧化反应。在可见光照射下,I_2的π路易斯酸性使其能够快速地与三键加成,然后与含有孤对电子的氧/氮原子发生亲电环化反应,实现C-O/C-N键的构筑,进一步的光催化加氧氧化实现产物生成和I_2再生。该可见光催化体系反应条件温和,只需催化量的碘,不需要其他任何牺牲剂和助催化剂,便可在2小时内高产率的生成一系列恶唑醛和吲哚醛衍生物,太阳光量子产率接近3%。对反应的中间体、碘物种、活性氧物种、光和I_2各自的作用等等,做了详细研究。机理研究发现,单线态氧在碘的催化循环中起了至关重要的作用。与以往的光敏剂不同,碘作为双功能光催化剂,一部分与反应底物加成并作为反应的中间体参与整个光催化循环过程,剩余的碘作为光敏剂。碘的这种新的光催化模式,将光催化和过渡金属催化的优点结合起来,拓展了太阳光光催化在有机合成领域的应用,有望实现传统过渡金属催化和光催化难以胜任的催化反应类型。
[Abstract]:Solar light and oxygen are green, pollution-free and inexhaustible resources, with solar light as light sources, oxygen as oxidants and highly selective chemical reactions that are challenging. However, under aerobic conditions, the active free radicals in the photocatalytic system may give priority to further loss of electrons or oxygenation. Oxidation, which leads to the degradation of the C-C fracture and the failure of the coupling reaction, uses photocatalytic to realize high selective coupling oxidation. In addition to factors such as the structure of the catalyst, the redox potential of the substrate and the solvent, the mode of action of the photocatalyst and the substrate and the kinetics of the reaction of the substrate must be considered. In this doctoral thesis, we constructed the photocatalytic system of coupling and oxygenation series reaction. Through dynamic control, we reasonably regulate the priority of coupling reaction and oxygenation reaction, and selectively make the coupling reaction precede oxygen oxidation, thus avoiding the over oxidation and other side reactions that lead to the C-C bond fracture. A series of efficient cyclization oxidation reactions, starting from a simple organic small molecule substrate, one step synthesis of four hydrogen naphtha lignin skeleton, cyclo peroxy compounds, VA zolal aldehyde, indolyl aldehyde and other organic compounds. The paper is divided into the following parts: Chapter 1, first briefly introduces the absorption and transformation of light energy, the basic concept and development of photocatalysis. The process, the classification, properties and principles of photocatalyst, and then a detailed overview of the various organic reactions of heterogeneous Semiconductor Photocatalysts (such as titanium dioxide) and homogeneous molecular type photocatalysts catalyzed under light conditions; on this basis, the advantages and disadvantages of various photocatalytic systems are summarized and prospected; finally, the doctoral thesis is established. In the second chapter, the second chapter, using titanium dioxide as a heterogeneous photocatalyst, as an oxidizing agent, successfully realized the photocatalytic epoxidation and oxidation of olefins without the need of additives and electronic sacrificial bodies, and synthesized a series of four naphthyl compounds. This compound is an important skeleton of the natural product of lignin. The [2+2] ring addition product, 1,2 two substituted cyclobutane, is a stable intermediate of the reaction. The structural data show that all of the reactions are trans configuration. The reaction of solar light photocatalyst has obtained good yield. The structure effect, solvent effect, reaction kinetics and photocatalytic mechanism of the catalyst have been studied in detail. The mechanism study shows that: This reaction involves two steps of alkene nucleophilic and oxygenated oxidation of free radical cation; if the free radical cations have sufficient chemical stability to fit the nucleophilic attack by another olefin molecule and selectively make the coupling reaction preferable to oxygen oxidation, the excessive oxygen that causes the C-C bond break is effectively avoided. In order to improve the efficiency of the cyclization reaction, the third chapter, in order to overcome the spatial steric resistance effect of 1,2 - two substituted olefins, realizes the high efficiency conversion of this kind of compound to four hydrogen naphthone products in the photocatalysis of titanium dioxide. In this chapter, we have adopted two strategies: (1) investigation of the intramolecular cyclization oxidation reaction of TiO_2 photocatalyst. The kinetic advantage of intramolecular reaction was used to overcome the spatial steric hindrance effect of the alkene beta substituent. (2) the [2+2] cyclization products of 1,2 - two substituted olefins were synthesized first, and then the reexpansion oxidation reaction was carried out under the photocatalytic condition of titanium dioxide. Based on this, a series of four hydrogen naphthone products were synthesized with high non enantioselectivity. The two step full synthesis of natural lignan (-) -8'-epi-aristoligone from basic raw materials was realized. The fourth chapter, in order to further expand the application of the solar photocatalytic epoxidation series reaction in the organic synthesis, we selected the iodine single substance with both visible light activity and PI Lewis acid instead of titanium dioxide. The cyclization oxidation reaction of propargidamide. Under visible light, I_2's PI Lewis acidity can be added quickly with the three bonds, and then electrophilic ring reaction with the oxygen / nitrogen atom containing the isolated electrons to realize the construction of the C-O/C-N bond and further photocatalytic oxygenation to achieve product generation and I_2 regeneration. The system has a mild reaction condition. A series of oxazole and indoles can be produced in a high yield in 2 hours without any other sacrificial agents and cocatalysts, and the yield of solar light quantum is close to 3%. for the reaction intermediates, iodine species, reactive oxygen species, light and I_2, and so on. The mechanism studies have found that the single state oxygen plays a vital role in the catalytic cycle of iodine. Unlike the previous photosensitizer, iodine is used as a bifunctional photocatalyst, a part of the reaction substrate is added to the reaction substrate and participates in the whole process of photocatalytic cycle. The remaining iodine is used as a photosensitizer. The combination of photocatalysis and transition metal catalysis has expanded the application of solar photocatalysis in the field of organic synthesis, and it is hopeful to realize the type of catalytic reaction which is unqualified for the traditional transition metal catalysis and photocatalysis.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O621.251;O644.1

【参考文献】