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Catalytic enantioselective hydrosilylation of pyridines and benzannulated congeners

吡啶和苯环化同系物的催化对映选择性氢化硅烷化

基本信息

批准号：
250883966
负责人：
Professor Dr. Martin Oestreich
金额：
--
依托单位：
Institut für Chemie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/250883966?language=en
关键词：
Catalytic enantioselective hydrosilylation pyridines benzannulated

项目摘要

The partial reduction of pyridines is a problem in synthetic chemistry not yet solved satisfactorily, also because conventional Birch reduction and state-of-the-art transition metal-catalyzed hydrogenation generally do not produce the desired dihydropyridine. Effective alternatives are chemoselective hydroboration and hydrosilylation, and several recently developed methods even allow for the regioselective transformation of pyridine itself and substituted pyridines into 1,2- and 1,4-dihydro-pyridines, respectively. The scope of these catalyses remained rather narrow though. Our laboratory now accomplished a highly 1,4-selective hydrosilylation that even allows for the 1,4-reduction of 4-substituted pyridines. Key to success was the cooperative activation of Si-H bonds at the polar Ru-S bond of a coordinatively unsaturated ruthenium(II) complex as catalyst. The cleavage of the Si-H bond yields a sulfur-stabilized silicon cation that is immediately sequestered by the pyridine nitrogen atom to afford a pyridinium ion. The ruthenium(II) hydride complex formed at the same time then reduces the pyridinium ion intermediate 1,4-selectively. This unusual regioselectivity now opens the opportunity to transform substituted pyridines with an additional substituent installed at the 4-position of the pyridine core into the corresponding asymmetrically substituted 1,4-dihydropyridines. The short-term objective of this project is the development of chiral ruthenium(II) catalysts that make an enantioselective hydride transfer onto prochiral 4-substituted pyridinium ions possible. The same principle will be extended to cognate quinolines (1,4-reduction) and appropriate isoquinolines (1,2-reduction). The long-term objective after establishment of the methodology (and during another potential funding period) could be the application of the obtained nitrogen-containing dihydroarenes in hitherto unprecedented enantioselective transfer hydrosilylations.

吡啶的部分还原是合成化学中尚未得到满意解决的问题，也是因为传统的Birch还原和目前最先进的过渡金属催化加氢通常不能产生所需的二氢吡啶。有效的替代方法是化学选择性硼氢化和硅氢化，最近发展的一些方法甚至允许吡啶本身和取代的吡啶分别区域选择性转化为1,2-和1,4-二氢吡啶。不过，这些催化剂的范围仍然相当狭窄。我们的实验室现在完成了一个高度选择性的1,4硅氢化反应，甚至允许4取代吡啶的1,4还原。成功的关键是作为催化剂的配位不饱和钌（II）配合物的极性Ru-S键上的Si-H键的协同活化。Si-H键的裂解产生硫稳定的硅阳离子，该阳离子立即被吡啶氮原子隔离以产生一个吡啶离子。同时形成的钌（II）氢化配合物选择性地还原了吡啶离子中间体1,4。这种不寻常的区域选择性使得在吡啶核心的4号位置附加取代基的取代吡啶转化为相应的不对称取代的1,4-二氢吡啶成为可能。该项目的短期目标是开发手性钌（II）催化剂，使对映选择性氢化物转移到前手性4取代吡啶离子上成为可能。同样的原则将扩展到同源喹啉（1,4-还原）和适当的异喹啉（1,2-还原）。建立该方法后（以及在另一个可能的资助期内）的长期目标可能是将所获得的含氮二氢芳烃应用于迄今为止前所未有的对映选择性转移硅化氢反应。