Efficient Methods for Asymmetric Synthesis Based on Asymmetric Transmission via Sigmatropic Rearrangements

本课题为期2年，主要研究成果如下：课题（1）“[2，3]-Wittig重排的不对称传递机理”：通过光学活性锡化合物生成的手性碳负离子末端的一系列实验，为不对称传递的“动态动力学拆分机理”提供了证据。课题（2）“[1，4]-Wittig重排的不对称传递”：首先，烯丙基内-和外-异丙基醚的碳负离子重排被发现主要经历罕见的[1，4]-Wittig重排，其以非立体特异性方式进行。第二，类似的（但在较低的温度下）重排烯丙基顺-香芹烯基醚和烯丙基反-胡椒基醚被证明进行[1，4]-维蒂希重排主要是进行完全保留的配置。有趣的是，-烯丙基顺式胡椒基醚的重排被发现进行[2，3]-Wittig重排排他。因此，基板构象已被揭示发挥关键作用，在确定这些碳负离子重排的周选择性。第三，发展了三种简便的方法，使烯丙基硅醚发生[1，4]-retero-Brook重排反应，得到硅烷基化的（2）-烯醇硅醚。主题（3）“通过顺序Sigmatropic重排的不对称传递”：研究了烯丙基环戊烯基醚的顺序[2，3]-Wittig/oxy-Cope重排反应。然而，还没有评估Sigmatropic序列的非对称传输的工作。

The main results of this 2-year project are as follows :Theme (1)"The Mechanism of the Asymmetric Transmission via [2,3]-Wittig Rearrangement" : A series of experiments using chiral carbanion termini generated from optically active tin compounds provided pieces of evidence in support of the "dynamic kinetic resolution mechanism" for the asymmetric transmission concerned.Theme (2)"Asymmetric Transmission via the [1,4]-Wittig Rearrangement" : First, the carbanion rearrangement of allyl endo-and exo-bornyl ether was found to predominantly undergo the rarely precedented [1,4]-Wittig rearrangement which proceeds in non-stereospecific manner. Second, similar (but at lower temperatures) rearrangements of allyl cis-carvenyl ether and allyl trans-piperityl ether were shown to undergo the [1,4]-Wittig rearrangement predominantly which proceeds with complete retention of configuration. Interestingly enough, the rearrangement of -allyl cis-piperityl ether was found to undergo the [2,3]-Wittig rearrangement exclusively. Thus, the substrate conformation has been revealed to play a key role in determining the periselectivity in these carbanion rearrangements. Third, three convenient procedures have been developed for effecting the [1,4]-retero-Brook rearrangement of allyl silyl ethers to afford the silylated (2)-enol silyl ethers.Theme (3)"Asymmetric Transmission via Sequential Sigmatropic Rearrangements" : the sequential [2,3]-Wittig/oxy-Cope rearrangement of allyl cyclopentenyl ether was investigated. However, no work for evaluating the asymmetric transmission of the Sigmatropic sequence has been made yet.