Light-Driven Enantioselective Organocatalysis
Light-Driven Enantioselective Organocatalysis
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DOI：
10.1002/anie.200901603
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发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Bach, Thorsten
中科院分区：
文献类型：
--
作者：
Mueller, Christiane;Bauer, Andreas;Bach, Thorsten
近年来，有机催化已成为现代催化的一个重要领域，它补充了金属催化和酶催化。[1]许多手性化合物以前不能通过其他转化以对映体纯净的形式制备，或者只有通过繁琐的反应序列才能获得。任何需要光化学而不是热激活的反应途径本质上是不可能被经典的有机催化剂催化的，除非光化学激活和催化过程分开。[3]在光能作为形成对映体选择性键的直接驱动力的过程中，需要设计手性有机催化剂来收集光，并允许通过能量或电子转移敏化底物。[4，5]在这一领域采用催化光诱导电子转移(30mol%的催化剂高达70%ee)的初步成功之后，[6]我们在此提出了一种手性有机催化剂，它结合了三重态能量转移的显著加速[7]和高的对映选择性。在所研究的测试反应(方案1)中，仅用10摩尔%的该催化剂就获得了90%的产率和92%的对映体选择性。由Kaneko等人首先描述的喹诺酮1的分子内[2+2]光环加成反应导致了两个区域异构体产物：主要的直产物2和交叉产物3。[8]这种特殊的转化被选为测试反应，因为它通过快速的五元环闭合产生环加成产物，[9]因为Krische等人[10]已经证明，手性二苯甲酮(19%ee，25mol%催化剂)可以敏化该反应。后者的结果提供了希望，即与前面描述的二苯甲酮4进行催化反应过程可能是可行的。
In recent years, organocatalysis has emerged as an important area of modern catalysis that complements metal catalysis and enzyme catalysis.[1] Many chiral compounds that could not be prepared previously in enantiomerically pure form by other transformations, or which were only obtained in tedious reaction sequences, were made accessible by organocatalytic reactions.[2] Nonetheless, there are still many product classes that are not available by conventional enantioselective organocatalysis. Any reaction pathway requiring photochemical but not thermal activation is inherently impossible to be catalyzed by a classical organocatalyst unless the process of photochemical activation and catalysis are separated.[3] Processes in which light energy serves as direct driving force for enantioselective bond formation require the design of chiral organocatalysts to harvest light and allow sensitization of the substrate by energy or electron transfer.[4, 5] After initial success in this area employing a catalytic photoinduced electron transfer (up to 70% ee with 30 mol% catalyst),[6] herein we present a chiral organocatalyst that combines a significant rate acceleration by triplet energy transfer [7] with high enantioselectivities. In the studied test reaction (Scheme1), a yield of 90% and an enantioselectivity of 92% ee were achieved with only 10 mol% of this catalyst.The intramolecular [2+ 2] photocycloaddition of quinolone 1, first described by Kaneko etal., leads to two regioisomeric products: the predominant straight product 2, and the crossed product 3.[8] This particular transformation was selected as test reaction, because it delivers a cycloaddition product by a rapid five-membered ring closure,[9] and because it had already been shown by Krische et al.[10] that a sensitization of this reaction is possible by a chiral benzophenone (19% ee with 25mol% catalyst). The latter result provided hope that a catalytic reaction course might be feasible with the benzophenone 4 described earlier.[6] The