Suginome Michinori, Iwanami Taisuke, Ohmori Yutaka, Matsumoto Akira, Ito Yoshihiko
Kyoto University, Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Katsura, Kyoto 615-8510,
Chemistry. 2005 May 6;11(10):2954-65. doi: 10.1002/chem.200401031.
Highly enantioenriched (E)-allylsilanes have been synthesized from optically active allylic alcohols on the basis of Pd-catalyzed intramolecular bis-silylation followed by highly stereospecific Si-O elimination reactions. The method involves three steps: 1) O-disilanylation of the allylic alcohols with chlorodisilanes, 2) intramolecular bis-silylation in the presence of a 1,1,3,3-tetramethylbutyl isocyanide/[Pd(acac)2] (acac = acetylacetonate) catalyst at 110 degrees C, and 3) treatment of the reaction mixture with organolithium reagents. The overall transformation proceeds with nearly complete conservation of the enantiopurity of the starting allyl alcohols by transposition of the C=C bond. For instance, (R)-(E)-3-decen-2-ol (99.6-99.7 % ee) produced (S)-(E)-4-(organosilyl)-2-decene of 98.8-99.4 % ee for a variety of silyl groups, including Me3Si, Me2PhSi, tBuMe2Si, Et3Si, and iPr3Si. In the bis-silylation step, the initially formed trans-1,2-oxasiletanes immediately dimerize to stereoselectively give 1,5-dioxa-2,6-disilacyclooctanes, which are isolated in high yield by carrying out the reaction at 70 degrees C. The eight-membered ring compounds undergo thermal extrusion of (E)-allylsilanes in high yield at 110 degrees C, along with formation of 1,3-dioxa-2,5-disilacyclohexane derivatives. These in turn undergo a Peterson-type elimination by treatment with nucleophiles such as BuLi and PhLi to give the (E)-allylsilanes. All of the steps involved in the sequence proceed with extremely high stereoselectivity and stereospecificity, leading to almost complete 1,3-chirality transfer through the overall transformation. The dimerization step, which forms diastereomeric intermediates, allows the synthesis of a highly enantioenriched allylsilane (99.4 % ee) from an optically active allylic alcohol with lower enantiopurity (79.2 % ee) by enrichment of enantiopurity. A general method for the determination of the enantiomeric excesses of (E)-allylsilanes is also described in detail.
基于钯催化的分子内双硅烷化反应，随后进行高度立体专一性的硅-氧消除反应，已从光学活性烯丙醇合成了高对映体富集的（E）-烯丙基硅烷。该方法包括三个步骤：1）烯丙醇与二氯硅烷进行O-二硅烷基化反应；2）在1,1,3,3-四甲基丁基异腈/[Pd(acac)₂]（acac = 乙酰丙酮）催化剂存在下，于110℃进行分子内双硅烷化反应；3）用有机锂试剂处理反应混合物。通过C=C键的迁移，整个转化过程几乎完全保留了起始烯丙醇的对映体纯度。例如，（R）-（E）-3-癸烯-2-醇（对映体过量99.6 - 99.7%）生成了（S）-（E）-4-（有机硅基）-2-癸烯，对于包括Me₃Si、Me₂PhSi、tBuMe₂Si、Et₃Si和iPr₃Si在内的多种硅基，其对映体过量为98.8 - 99.4%。在双硅烷化步骤中，最初形成的反式-1,2-氧杂硅环丁烷立即二聚，立体选择性地生成1,5-二氧杂-2,6-二硅杂环辛烷，通过在70℃进行反应可高产率地分离得到。八元环化合物在110℃下高产率地发生热挤出反应生成（E）-烯丙基硅烷，同时形成1,3-二氧杂-2,5-二硅杂环己烷衍生物。这些衍生物再通过用亲核试剂如BuLi和PhLi处理进行彼得森型消除反应，得到（E）-烯丙基硅烷。该序列中涉及的所有步骤都具有极高的立体选择性和立体专一性，导致在整个转化过程中几乎完全实现1,3-手性转移。形成非对映体中间体的二聚步骤使得能够通过对映体纯度的富集，从对映体纯度较低（79.2% ee）的光学活性烯丙醇合成高对映体富集的烯丙基硅烷（99.4% ee）。还详细描述了一种测定（E）-烯丙基硅烷对映体过量的通用方法。
