Catalytic Activation of Skeletal Bonds in Strained Photoproducts

有机分子中骨架键（特别是C-C和C-N）的活化对于有效合成新型分子框架具有很高的潜力。然而，由于能量的原因，这种键活化难以进行。它们通常需要螯合部分与反应性（并且大多是昂贵的）过渡金属催化剂或应变反应物组合。后一种底物可以通过光化学转化从容易获得的起始材料容易地制备。本项目的目的是寻找新的应变光产物的催化键活化，其机理研究以及探索其在杂环框架合成中的适用性，杂原子（特别是氧和氮）的引入将提供额外的活化以及对键活化的区域控制。除了具有纯稳定光产物的经典分批程序外，还应研究流动光反应器中产生的短寿命中间体的反应。迄今为止，只有少数光化学产生的高能化合物进行了这种键活化，特别有吸引力的分子间反应在很大程度上未被研究。尽管如此，一般概念的实用性可以在初步研究中得到证明，并且已经开发了两种新颖的咪唑和吡咯的合成方法。理想情况下，所提出的方法允许通过采用紫外光作为唯一能量来源来构建有吸引力的分子支架，同时以可持续的方式避免形成低能量的副产物（例如金属盐，硼酸衍生物）。

The activation of skeletal bonds (in particular C-C and C-N) in organic molecules has a high potential for the efficient synthesis of novel molecular frameworks. Due to energetic reasons, such bond activations are, however, difficult to perform. They usually require chelating moieties in combination with reactive (and mostly pricy) transition metal catalysts or strained reactants. The latter substrates can be easily prepared from readily available starting materials by photochemical transformations. The aim of the present project is the search for novel catalytic bond activations of strained photoproducts, their mechanistic investigation as well as the exploration of their applicability for the synthesis of heterocyclic frameworks.The inclusion of heteroatoms (in particular oxygen and nitrogen) will provide additional activation as well as regiocontrol for the bond activations. In addition to classical batch-procedures with pure stable photoproducts, reactions of short-lived intermediates generated in flow photoreactors shall also be investigated. Only few photochemically generated high-energy compounds have been subjected to such bond activations so far and the particularly attractive intermolecular reactions are largely underinvestigated. Nevertheless, the practicability of the general concept could be demonstrated in preliminary investigations and two novel syntheses of imidazoles and pyrroles have already been developed.Ideally, the projected methodology permits the construction of attractive molecular scaffolds by employing UV-light as the sole energy source while avoiding the formation of low-energy co-products (e.g. metal salts, boric acid derivatives) in a sustainable approach.