From mesomeric betaines to anionic N-heterocyclic carbenes

介体甜菜碱是阴离子杂环卡宾的多用途前体。然而，它们的合成潜力远远没有被开发出来。通过去质子化，可以生成极富pi电子的阴离子N-杂环卡宾，根据共轭类型的不同，它也可以在卡宾碳原子上具有高的pi电子密度。在对合成酮和芳香酮进行初步研究后，本项目将另外四个中间体甜菜碱作为N-杂环卡宾的前体，它们的pi-结构不同。它们是通过它们的CREF值来选择的，最近引入的CREF值是为了量化合适的前体形成卡宾的难易程度。文中还将讨论CREF值与TEP值、HEP值、1JCSe耦合常数等之间的相互关系。捕集反应(Se，S)，络合物(Rh，Pd，Pt，Au，Ir，…)，并将进行催化活性的检查。令人惊讶的是，辛酮-卡宾的二氧化碳加合物在酸中催化Suzuki-Miyaura反应。将研究这种交叉偶联在碱不稳定的底物上的应用，如氨基酸和二肽(它们很容易与碱消旋)和异恶唑以及苯并异唑(它们遭受与碱的快速环断裂)。

Mesomeric betaines are versatile precursors of anionic heterocyclic carbenes. However, their synthetic potential is far from being exploited. By deprotonation, extremly pi-electron-rich anionic N-heterocyclic carbenes can be generated which also - depending on the type of conjugation – can possess high pi-electron densities on the carbene carbon atom. After preliminary work on sydnones and münchnones, this project deals with four additional mesomeric betaines as precursors of N-heteroccylic carbenes, which differ in their pi-architectures. They have been chosen by their CREF values, which have been introduced recently to quantify the ease of carbene formation from suitable precursors. The translation of the CREF values into chemistry and their relationship to TEP and HEP values, 1JCSe coupling constants and others will be discussed. Trapping reactions (Se, S), complexations (Rh, Pd, Pt, Au, Ir, …), and examinations of the catalytic activities will be performed. Surprisingly, the carbon dixide adducts of sydnone-carbenes catalyze Suzuki-Miyaura reactions in acids. The application of this cross-coupling to base-labile substrates such as amino acids and dipeptides (which racemate easily with bases) and isoxazoles as well as benzisoazoles (which suffer from rapid ring-cleavages with bases) will be studied.