Asymmetric Organic Synthesis Via New Enantioenriched Allylsilanes

通过钯催化的烯丙醇分子内双硅基化反应，立体选择性合成了具有ω-羟基的高度富集对映体的烯丙硅烷。新的功能化烯丙基硅烷在路易斯酸的存在下与醛反应，通过缩醛化反应得到环醚，然后进行分子内细井-樱井反应。在其γ-烷基上有ω-羟基的烯丙基硅烷对3-（1-烯基）基的2-取代环醚具有立体选择性。例如，(S)-(E)-6-（二甲基苯基硅基）十二-4-烯-1-醇（93% ee）和(R)-(E)-7-（二甲基苯基硅基）十一-5-烯-1-醇（96% ee）与庚醛反应分别产生反式-2-己基-3-（（E)-1-己基）四氢吡喃（92% ee）和反式-2-己基-3-(E)-1-己基）氧环烷（94% ee），产率良好，立体守恒率为bb0 97%。另一方面，α-烷基链上带有ω-羟基的烯丙基硅烷具有立体选择性地提供2,3 -二取代氧环烷-4。在这些反应中，不仅实现了高非对映选择性，而且实现了高立体选择性手性从烯丙硅烷到环醚的转移。

Highly enantioenriched allylsilanes bearing an ω-hydroxy group were synthesized stereoselectively via a sequence involving palladiumcatalyzed intramolecular bis-silylation of allylic alcohols. The new functionalized allylsilanes reacted with aldehydes in the presence of Lewis acids, giving cyclic ethers via acetalization followed by intramolecular Hosomi-Sakurai reaction. The allylsilanes with an ω-hydroxy group on their γ-alkyl group afforded 2-substituted cyclic ethers with 3-(1-alkenyl) group stereoselectively. For instance, reactions of (S)-(E)-6-(dimethylphenylsilyl) dec-4-en-1-ol (93% ee) and (R)-(E)-7-(dimethylphenylsilyl) undec-5-en-1-ol (96% ee) with heptanal afforded trans-2-hexyl-3-((E)- 1-hexenyl) tetrahydropyran (92% ee) and trans-2-hexyl-3-((E)-1-hexenyl) oxepane (94% ee), respectively, in good yields with >97% stereoconservation. On the other hand, allylsilanes with an ω-hydroxy group on their α-alkyl chain afforded 2, 3-disubstituted oxacycloalk-4-enes stereoselectively. In these reactions, not only high diastereoselectivity but also highly stereoselective transfer of chirality from the allylsilanes to the cyclic ethers was accomplished.