Abstract：
Our recent efforts to develop novel N-Heterocyclic carbene (NHC)-catalyzed asymmetric reactions are described. During our investigation for development of the acylation reactions via acylazoliums generated by the reactions of NHCs and α-oxidized aldehydes, we have observed significant effects of substitution at a remote site of the carbene carbon of NHCs. In addition, we also observed a significant enhancement of the enantioselectivity by the addition of carboxylate anions. From this observation, we proposed a novel working hypothesis involving a formation of a complex of the substrate and additive to reinforce the recognition of the catalyst for enhancement of the catalytic performance of the asymmetric N-heterocyclic carbene system. By applying this concept, we achieved the kinetic resolutions of both cyclic and acyclic alcohols in excellent enantioselectivities. The effects of the remote substitution were also observed in intramolecular Stetter reaction and intermolecular benzoin reaction. In these reactions, the comparison of the catalytic performance of the NHCs bearing variable remote substitutions provided insights into the reaction mechanism because the remote substitution tuned the electronic nature of NHCs without affecting the steric and electrostatic factors around the reaction site. We also developed an intramolecular benzoin condensation involving two aldehydes, which is challenging to realize. Using the substrates bearing proper protecting groups, we succeeded in the stereo divergent synthesis of a variety of inososes, which are important intermediates for the synthesis of biologically active cyclitols.
摘要：
描述了我们最近开发新型N-杂环卡宾（NHC）催化的不对称反应的努力。在我们研究通过NHCs和α-氧化醛的反应产生的酰基唑来发展酰化反应的过程中，我们已经观察到在NHC的卡宾碳的偏远位置处取代的显着影响。此外,我们还观察到通过添加羧酸根阴离子显着提高了对映选择性。从这个观察,我们提出了一个新的工作假设，涉及底物和添加剂的复合物的形成，以增强对催化剂的识别，以增强不对称N-杂环卡宾体系的催化性能。通过应用这个概念，我们以优异的对映选择性实现了环醇和无环醇的动力学拆分。在分子内Stetter反应和分子间苯偶姻反应中也观察到了远程取代的影响。在这些反应中,具有可变远程取代的NHC的催化性能的比较提供了对反应机理的见解，因为远程取代调节了NHC的电子性质，而不影响反应位点周围的空间和静电因素。我们还开发了一种涉及两种醛的分子内安息香缩合反应，这是具有挑战性的实现。使用带有适当保护基团的基材，我们成功地立体发散合成了多种肌酸激酶，它们是合成生物活性环醇的重要中间体。
