利用可见光能源实现天然气体作原料到高附加值化学品的合成转化

Organic synthesis employing visible-light as clean energy source promises to be a green and sustainable area of research. Light activation of molecules provides access to reaction pathways that are otherwise impossible to reach with classical thermochemical activation. However, development in this area is just at the beginning stage, and reports on visible-light-promoted synthesis using gaseous feedstocks are rare. The use of natural gases to generate valuable chemicals is of great concern from an economic and environmental standpoint, as they represent the most inexpensive chemical feedstocks, and are readily removed after reactions, affording cleaner synthetic processes. However, there is a general reluctance to utilize natural gases in synthetic laboratories under visible-light-irradiation condition mainly due to lack of convenient, safe and effective reaction apparatus. The proposed research aims to develop transformations assisted by novel flow apparatus including our recent developed continuous-flow micro-tubing reactor, “stop-flow” micro-tubing reactor, and proposed “lotus-type” flow reactor that convert visually unlimited gas feedstocks (such as CO2, ethylene, ethane, and methane) to valuable fine chemicals. CO2 will be utilized for carboxylation of alkynes and amines to access various pharmaceutically important heterocycles and amino acids. Visible-light-mediated ethylene difunctionalization will be investigated by merging photoredox catalysis and transition-metal-catalysis. Methane and ethane will be applied as C1 and C2 synthons to assemble complex molecules via photo C-H activation. A centerpiece of the proposed research will rely on the unique advantages provided by the novel flow platforms, which is extremely useful for both academic and industrial application.

可见光是无尽的清洁能源，可见光驱动的有机合成符合绿色可持续化学发展的需求。有机小分子通过光激发能进行热激发所无法实现的反应模式，但其研究仍处在萌芽阶段。利用天然气体合成高附加值化学产品具有非常诱人的环保和经济价值。天然气体不仅非常廉价，在反应后非常容易与产品分离提纯。然而由于实验室传统条件没有高效安全而又操作简易的反应装置能够满足在光条件下利用气体进行合成科研的要求，使得此研究领域大大受限。本课题旨在利用申请人独立课题组近两年开发的微管流动反应器，微管“停流”反应器和拟开发的藕式流动反应器作为平台，开发在可见光条件下将天然气体原料转化为高附加值化学品的方法学。包括在光照条件下利用二氧化碳与炔烃和胺类物质合成具有生物活性的杂环化合物和氨基酸，对乙烯进行双官能团化，和利用甲烷和乙烷进行碳氢活化。本课题的研究基于新型微流反应器所提供的可靠平台，具有极高的理论研究和实际工业应用价值。

以廉价易得的气体为化工原料，高效绿色合成一系列高附加值的精细化学品一直是精细化工的追求目标。本项目基于可见光催化的策略，以廉价易得的气体为原料，发展了一系列新型绿色的合成方法学，高效合成一系列高附加值化合物，并成功地将这些方法学应用于天然产物、药物和农药活性分子的后期官能团修饰中。具体内容如下：1. 以乙烯为原料，1）实现了光致氧化还原协同镍催化的乙烯的双官能团化反应和还原Heck反应，2）实现了可见光诱导的无金属参与的乙烯的芳基-二氟烷基化反应；2. 以烷烃为原料，实现了光致氧化还原协同氢原子转移催化惰性C(sp3)-H键与杂芳香烃的C(sp2)-H键的放氢交叉偶联反应，值得一提的是，该方法成功实现乙烷气体小分子的C(sp3)-H键的官能团化；3. 以二氟氯甲烷为原料，实现了光致氧化还原协同卤原子转移催化非活化烯烃的二氟甲基化反应；4. 利用廉价的醛为原料，实现了可见光诱导的溴自由基氢原子转移催化醛与烯烃的加成反应和醛C-H键的氢氘交换反应；5. 以吡啶-N-氧化物为原料，实现了光致氧化还原催化炔烃的烷基化/酰基化反应。该项目的实施，推动了可见光催化的气体分子的官能团化反应的研究领域进一步发展，为将来的工业应用提供相关理论技术支持。