Revealing the mechanisms of titanium-catalyzed umpolung reactions by a combined experimental and theoretical approach

钛(III)催化的还原反应提供了一种很好的途径来获得碳-碳键，而这些碳-碳键是其他方法无法直接形成的。在我们以前对酮-腈和烯酮-腈偶联反应研究的基础上，我们将通过实验工作和密度泛函理论计算相结合的方法来研究这些反应的机理。主要目标是执行和理解催化循环的各个部分，并开发关键步骤的模型，特别是C-C键形成事件。阳离子中间体的作用和第二个钛(III)物种的参与将被详细研究。此外，我们的目的是为我们在先前发表的不对称环化反应中观察到的高选择性提供解释。首先，提供了支持研究计划每个单独部分的可行性的结果。该项目的结论将对该领域的新反应和催化剂的开发产生重大影响。它们将提供对还原Upolung反应的一般了解，并极大地促进这一研究领域的未来研究。

Titanium(III)-catalyzed reductive umpolung-reactions provide an elegant access to carbon-carbon bonds that cannot be formed in a direct fashion by other methods. Based on our previous works on ketone-nitrile and enone-ennitrile couplings, we will investigate the mechanisms of such reactions by a combination of experimental works and DFT-calculations. The main goal is to perform and understand the individual parts of the catalytic cycles and to develop models for the key-steps, especially the C-C bond forming events. The role of cationic intermediates and the participation of a second titanium(III)-species will be investigated in detail. In addition, it is our aim to provide an explanation for the high selectivities that we observed in our previously published enantioselective ketonitrile cyclization reaction. First results are provided that support the feasibility of each individual part of the research program. The conclusions from this project will have a major impact on the development of new reactions and catalyst generations in this field. They will provide a general understanding of reductive umpolung reactions and greatly facilitate future investigations in this research area.