Chiral Dienolate Chemistry in Remote Asymmetric Induction

虽然基于手性助剂的不对称诱导构成了最常用于不对称合成的基本原理，但是在由手性助剂赋予的不对称环境之外的位置处的不对称诱导当然是极其困难的。然而，从概念上讲，这个问题可以通过在不对称环境内的不对称感应过程与不对称传输过程的适当组合来解决，以实现网络远程不对称感应。我们设计了一种通用的合成方法，该方法依赖于手性二烯醇化物化学用于不对称诱导，然后是σ迁移过程用于不对称传递。研究结果如下：（1）由手性α、β或β、γ-不饱和酰亚胺衍生的二烯醇化物的烯丙基化，然后进行科普重排，可以影响净远程不对称诱导，从而在高% de的γ位置产生任一构型的新手性。该方法的实用性在萨拉戈萨酸A的C6侧链的不对称合成中示出。(2)衍生自手性α，β-或β，γ-不饱和酰亚胺的硼二烯醇化物的不对称羟醛缩合反应，随后进行C-Cope重排，显示出提供γ，δ-反式或-顺式-α，β-不饱和酰亚胺作为主要产物。

While the chiral auxiliary-based asymmetric induction constitutes the underlying principle most often utilized for asymmetric synthesis, the asymmetric induction at a position beyond the asymmetric environment imparted by the chiral auxiliary is, of course, extremely difficult. Conceptually, however, this problem could be solved by the proper combination in tandem of an asymmetric induction process within the asymmetric environment with an asymmetric transmission process to effect the net remote asymmetric induction.To realize this concept, we designed a general synthetic approach which relies upon the chiral dienolate chemistry for the asymmetric induction followed by the sigmatropic process for the asymmetric transmission.A summary of the research results is as follow :(1) The allylation of the dienolate derived from the chiral alpha, beta- or beta, gamma-unsaturated imide followed by the Cope rearrangement is shown to effect the net remote asymmetric induction to create a new chirality of either configuration at the gamma-position in high % de. The utility of this approach is shown in the asymmetric synthesis of the C6 side chain of zaragozic acid A.(2) The asymmetric aldol reaction of the boron dienolate derived from chiral alpha, beta- or beta, gamma-unsaturated imide followed by the siloxy-Cope rearrangement is shown to provide the gamma, delta-anti-or-syn-alpha, beta-unsaturated imide as the main product.