Asymmetric Organic Synthesis Via New Enantioenriched Allylsilanes

通过钯催化的烯丙醇分子内双硅烷化反应，立体选择性地合成了高对映体富集的含ω-羟基的烯丙基硅烷。在刘易斯酸存在下，新型功能化烯丙基硅烷与醛反应，通过缩醛化和分子内Hosomi-Sakurai反应生成环醚。γ-烷基上带有ω-羟基的烯丙基硅烷立体选择性地合成了3-（1-烯基）-2-取代环醚。例如，（S）-（E）-6-甲基-IH-吡唑的反应是优选的。（二甲基苯基甲硅烷基）癸-4-烯-1-醇（93%ee）和（R）-（E）-7-（二甲基苯基甲硅烷基）癸-4-烯-1-醇（93%ee）。（二甲基苯基甲硅烷基）十一碳-5-烯-1-醇（96%ee）与庚醛反应分别得到反式-2-己基-3-（（E）-1-己烯基）四氢吡喃（92%ee）和反式-2-己基-3-（（E）-1-己烯基）氧杂环庚烷（94%ee），产率良好，立体保守性>97%。而α-烷基链上带有ω-羟基的烯丙基硅烷则立体选择性地合成了2，3-二取代氧杂环烷烃-4-烯。在这些反应中，不仅实现了高的非对映选择性，而且实现了手性从烯丙基硅烷到环醚的高立体选择性转移。

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.