Development of Novel Catalyses Based on Base-Activated Silicates

硅原子由于其空的3 - d轨道，扩大了配位球，形成了相对稳定的五或六配位化合物，或称“高价硅酸盐”。由于这些外配位物质是具有丰富反应活性的强大中间体，因此基于这一独特机制的各种有机反应都取得了显著进展。我们研究了碱促进的不对称催化，其中碱与硅原子配位形成高价硅酸盐。我们发现手性二萘酸锂催化了三甲氧基硅烯醇醚的醛缩反应，实现了用四取代硅烯醇醚构建季碳中心。在此方案下，采用不对称醛醇反应构建季碳中心的联抗选择性最高。我们还发现手性膦氧化物催化了三氯硅烯醇醚的醛醇反应，其中产物的非对映比（synlanti）与三氯硅烯醇醚的几何形状（E/Z）之间存在完全的立体化学相关性。该方法推广到直接醛醇反应，即两个羰基化合物之间的醛醇反应，不使用硅烯醇醚作为醛醇供体。膦氧化物与四氯硅烷配位可产生比四氯硅烷更多的酸配合物，这些酸配合物在Lewis酸催化的不对称反应中得到有效利用。根据这一概念，手性膦氧化物的催化量激活了四氯硅烷，促进了醛与三烷基的阿布拉莫夫型膦化反应，产生了相应的羟基膦酸盐，这是该反应的第一个不对称版本。

Silicon atom expands its coordination sphere to give relatively stable penta- or hexa-coordinated compound, or "hypervalent silicate" due to its vacant 3d-orbital. Since these extracoordinated species are powerful intermediates with abundant reactivities, remarkable developments have been made on various organic reactions based on this unique mechanism. We investigated the base-promoted asymmetric catalyses wherein bases coordinated with silicon atoms to form hypervalent silicates. We found that chiral lithium binaphtholate catalyzed the aldol reaction of trimethoxysilyl enol ethers, which realized the construction of quaternary carbon center using tetra-substituted silyl enol ethers. With this protocol, the highest synlanti selectivity was obtained in the construction of quaternary carbon center using asymmetric aldol reaction. We also found that chiral phosphine oxides catalyzed the aldol reaction of trichlorosilyl enol ethers, wherein complete stereochemical correlation is observed between the diastereomeric ratio (synlanti) of the products and the geometries (E/Z) of the trichlorosilyl enol ethers. This methodology was extended to the direct aldol reaction, the aldol reaction between two carbonyl compounds, not using silyl enol ether as an aldol donor. Phosphine oxides coordinated with tetrachlorosilane to afford more acids complexes than tetrachlorosilane itself, which were efficiently utilized in Lewis acid-catalyzed asymmetric reactions. With this concept, catalytic amounts of chiral phosphine oxides activated tetrachlorosilane to promote the Abramov-type phosphonylations of aldehyde with trialkyl affording the corresponding hydroxyphophonates, which exhibited the first asymmetric version of this type of reaction.