Asymmetric photoredox transition-metal catalysis activated by visible light
Asymmetric photoredox transition-metal catalysis activated by visible light
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DOI：
10.1038/nature13892
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发表时间：
2014-11-06
期刊：
影响因子：
64.8
通讯作者：
Meggers, Eric
中科院分区：
文献类型：
--
作者：
Huo, Haohua;Shen, Xiaodong;Meggers, Eric
不对称催化被认为是满足精细化工和制药工业对对映体纯小分子日益增长的需求的最经济的策略之一（1）。可见光被认为是一种环境友好和可持续的能源形式，用于引发化学转化和催化化学过程（2-5）。由于这些原因，可见光驱动的催化不对称化学是当前非常感兴趣的主题（2-5）。光氧化还原催化提供了在令人惊讶的温和反应条件下产生具有通常不寻常或非常规反应性的高反应性自由基离子中间体的机会（6）。在这样的系统中，光活化的敏化剂引发来自（或到）封闭壳层有机分子的单电子转移以产生自由基阳离子或自由基阴离子，其反应性然后被用于感兴趣的或不寻常的化学转化。然而，光激发底物、中间自由基离子或自由基的高反应性以及后续反应的低活化势垒为开发在立体化学控制下工作并以不对称方式提供手性分子的有效催化光化学过程提供了重大障碍（7）。在这里，我们报告了一种高效的不对称催化剂，使用可见光进行必要的分子活化，从而结合了不对称催化和催化剂。我们发现，手性铱配合物可以作为光敏剂的光氧化还原催化，并在同一时间提供非常有效的不对称诱导2-酰基咪唑的对映选择性烷基化。这种新型的不对称光氧化还原催化剂，其中金属中心同时作为手性、催化活性的刘易斯酸中心和光氧化还原中心的唯一来源，为非外消旋手性分子的“绿色”合成提供了新的机会。
Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries(1). And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes(2-5). For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest(2-5). Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions(6). In such systems, photoactivated sensitizers initiate a single electron transfer from(or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion(7). Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the 'green' synthesis of non-racemic chiral molecules.