Development of Novel Catalyses Based on Base-Activated Silicates

硅原子的3d轨道空位使其配位范围扩大，形成相对稳定的五配位或六配位化合物，即“超价硅酸盐”。由于这些配位物种是具有丰富反应活性的强有力的中间体，基于这种独特机理的各种有机反应已经取得了显着的发展。我们研究了碱促进的不对称催化剂，其中碱与硅原子配位形成高价硅酸盐。我们发现手性联萘锂催化三甲氧基硅烯醇醚的羟醛缩合反应，实现了四取代硅烯醇醚构建季碳中心。在此条件下，不对称羟醛缩合反应构筑季碳中心的合成选择性最高。我们还发现，手性氧化膦催化三氯硅烯醇醚的羟醛缩合反应，产物的非对映异构体比例（synlanti）与三氯硅烯醇醚的几何构型（E/Z）之间存在完全的立体化学相关性.这种方法被扩展到直接羟醛缩合反应，两个羰基化合物之间的羟醛缩合反应，不使用甲硅烷基烯醇醚作为羟醛缩合供体。氧化膦与四氯硅烷配位形成的酸类配合物比四氯硅烷本身的酸类配合物多，可有效地用于刘易斯酸催化的不对称反应。基于这一概念，催化量的手性氧化膦活化四氯硅烷，促进醛与三烷基的Abramov型膦酰化反应，得到相应的羟基膦酸酯，这是该类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.