Development of Novel Catalyses Based on Base-Activated Silicates

硅原子扩大了它的配位范围，得到了相对稳定的五配位或六配位化合物，或“高价硅酸盐”，因为它的3D轨道是空的。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，基于这一独特的反应机理，在各种有机反应中取得了显著的进展。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超价硅酸盐。我们发现，手性联萘酚锂催化了三甲氧基硅烯醇醚的Aldol反应，实现了四取代硅烯醇醚的季碳中心构筑。该方法在利用不对称Aldol反应构建季碳中心时获得了最高的合成选择性。我们还发现，手性膦氧化物催化了三氯硅烯醇醚的Aldol反应，其中产物的非对映异构体比(Synlanti)与三氯硅基烯醇醚的几何构型(E/Z)之间存在完全的立体化学关联。这种方法被扩展到直接的羟醛反应，即两个羰基化合物之间的羟醛反应，而不是使用硅烯醇醚作为羟醛供体。膦氧化物与四氯硅烷配位形成了比四氯硅烷本身更多的酸性络合物，在Lewis酸催化的不对称反应中得到了有效的利用。有了这个概念，催化量的手性膦氧化物激活了四氯硅烷，促进了醛与三烷基的阿布拉莫夫式的膦酰化反应，得到了相应的羟基膦酸酯，这是这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.