Catalytic Activation of Skeletal Bonds in Strained Photoproducts

有机分子中骨架键(特别是C-C和C-N)的活化对于高效合成新型分子骨架具有很高的潜力。然而，由于能量方面的原因，这样的键激活很难执行。它们通常需要螯合部分与反应性(且大多是昂贵的)过渡金属催化剂或应变反应物相结合。通过光化学转化，可以很容易地从现成的起始材料中制备后一种衬底。本项目的目的是寻找新的应变光产物的催化键活性，对其机理进行研究，并探索其在合成杂环骨架中的适用性。杂原子(特别是氧和氮)的加入将为键的活化提供额外的活化和区域控制。除了使用纯稳定光产物的经典间歇过程外，还应研究流动光反应器中产生的短寿命中间体的反应。到目前为止，只有很少的光化学生成的高能化合物受到这种键的激活，特别吸引人的分子间反应在很大程度上还没有得到充分的研究。然而，一般概念的实用性可以在初步研究中得到证明，已经开发出两种咪唑和吡咯的新合成方法。理想的是，该方法允许通过使用紫外光作为唯一能源来构建有吸引力的分子支架，同时避免以可持续的方法形成低能量的副产物(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.