Developemt of Asymmetric Carbanion Rearrangements with High Stereoselection

本课题的主要研究成果如下：(1)研究了手性2-恶唑啉生成的手性锂和氮烯酸钾末端的不对称[2，3]-Wittig重排反应。我们发现，这些重排提供了相对较高的光学产率(78-95%ee)。在这些研究中，我们观察到了反阳离子(Li与K)及其与冠醚的络合作用的有趣影响。此外，该不对称反应还成功地应用于非天然马鞭草素内酯的手性合成。(2)研究了手性酰胺Li-和Zr(&lt；IV&gt；)-烯醇端的不对称[2，3]-Wittig重排反应。不幸的是，这些不对称变体被发现只能提供中等水平的不对称诱导。然而，有趣的是，与锂-烯醇型…相比，锆烯醇型变异体表现出相反的非对位面选择意义(3)详细研究了8-苯基薄荷醇衍生手性酯体系生成的手性酯烯醇端的不对称[2，3]-Wittig重排反应。首先，我们发现锂-烯酸重排提供了极高的光学产率(&gt；95%ee)和高的红光选择性(&gt；90%)。因此，这种不对称重排反应为手性合成α-羟基-β-烷基羧酸衍生物提供了一种有效的方法。它的有效性已经在简单的魔芋内酯的手性合成中得到了证明。第二，硅烯醇醚通过转位生成的钛(&lt；IV&gt；)-和锡(&lt；IV&gt；)-烯醇酸酯的重排反应表现出很低的不对称诱导水平。第三，在上述结果的基础上，我们讨论并阐明了[2，3]-Wittig重排反应中涉及的金属烯醇酸盐的结构。较少

The main results of this project are summarized as follows.(1) Asymmetric [2,3]-Wittig rearrangement involving chiral lithium and potassium azaenolate termini generated from chiral 2-oxazolines have been investigated. We found that these rearrangements provided relatively high optical yields (78-95% ee). During these studies, we have observed interesting influences of the countercation (Li vs. K) and their complexation with a crown ether. Furthermore, the asymmetric reaction has successfully been applied to the chiral synthesis of unnatural verrucarinolactone.(2) Asymmetric [2,3]-Wittig rearrangement involving chiral amide Li- and Zr( <IV> )-enolate termini generated from the prolinol- and valinol-derived amide systems has been studied. Unfortunately, these asymmetric variants have been found to provide only moderate levels of asymmetric induction. Interestingly, however, the Zr-enolate variant has been shown to the opposite sense of diastereofacial selection to that of the Li-enolate … More counterpart.(3) Asymmetric [2,3]-Wittig rearrangement involving chiral ester enolate termini generated from the 8-phenylmenthol-derived chiral ester system has been investigated in details. First, we have found that the Li-enolate rearrangement provides an extremely high optical yields (>95% ee) along with a high erythro-selectivity (>90%). Thus, this type of asymmetric rearrangement offers an efficient method for chiral synthesis of <alpha> -hydroxy- <beta> -alkyl carboxylic acid derivatives. Its efficiency has been demonstrated within the simple chiral synthesis of verrucarinolactone. Second, the rearrangement involving Ti( <IV> )- and Sn( <IV> )-enolates generated from the silyl enol ether via transmetalation has been found to exhibit very low levels of asymmetric induction. Third, the rearrangement involving Zr( <IV> )-enolate generated from the Li-enolate via transmetalation, by contrast, provides a high optical yield comparable to that of the Li-enolate counterpart.On the basis of these results described above, we have discussed and elucidated the structures of the metal enolates involved in the [2,3]-Wittig rearrangements. Less