Hasegawa Shingo, Soga Kosuke, Motokura Ken
Department of Chemistry and Life Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
JACS Au. 2025 Mar 17;5(4):1914-1921. doi: 10.1021/jacsau.5c00140. eCollection 2025 Apr 28.
Catalytic reduction of carboxylic acids to the corresponding alcohols is a challenging but useful reaction. Since the conventional reduction methods such as hydrogenation and hydrosilylation largely rely on transition-metal catalysts, the development of heterogeneous organocatalysts for the reaction is an attractive research target. In this study, we achieved the reduction of benzoic acid derivatives to benzylic alcohols by hydrosilylation with a silica-immobilized cyclic urea catalyst followed by hydrolysis. The catalytic activity of immobilized cyclic urea was significantly higher than that of the free cyclic urea, silica supports, their physical mixture, or immobilized organocatalysts with different structures, such as cyclic carbonates and amines. Control experiments and Fourier transform infrared (FT-IR) spectroscopy revealed that the synergy between immobilized urea and silanol groups on the silica surface resulted in superior catalysis and that hydrosilylation of the silyl ester intermediate was the key step. It was proposed that urea and silanol concertedly activate the hydrosilane and silyl ester, respectively, to achieve efficient hydride transfer, which was supported by density functional theory (DFT) calculations on model reaction systems. This study demonstrates that the concerted activation of nucleophiles and electrophiles by silica-immobilized organocatalysts is effective for challenging molecular transformations.
将羧酸催化还原为相应的醇是一个具有挑战性但很有用的反应。由于传统的还原方法如氢化和硅氢化主要依赖于过渡金属催化剂，因此开发用于该反应的非均相有机催化剂是一个有吸引力的研究目标。在本研究中，我们通过用硅胶固定的环状脲催化剂进行硅氢化反应然后水解，实现了苯甲酸衍生物向苄醇的还原。固定化环状脲的催化活性明显高于游离环状脲、硅胶载体、它们的物理混合物或具有不同结构的固定化有机催化剂，如环状碳酸酯和胺。对照实验和傅里叶变换红外（FT-IR）光谱表明，硅胶表面固定化脲和硅醇基团之间的协同作用导致了优异的催化性能，并且甲硅烷基酯中间体的硅氢化是关键步骤。有人提出，脲和硅醇分别协同活化硅烷和甲硅烷基酯，以实现有效的氢化物转移，这得到了模型反应体系的密度泛函理论（DFT）计算的支持。这项研究表明，硅胶固定化有机催化剂对亲核试剂和亲电试剂的协同活化对于具有挑战性的分子转化是有效的。
