An enantioselective approach to construction of the complex framework of the CP compounds is presented. The synthesis relies on initial elaboration of the two sidechains. The "upper" appendage was asymmetrically dihydroxylated with both AD-mix reagents in order to lend flexibility to the scheme and provide the necessary handle for evolving the additional stereogenic centers. These fragments were linked to benzoic acid via Birch reduction-alkylation and subsequent cuprate addition. A series of functionalization reactions including dissolving metal reduction, Claisen rearrangement, iodolactonization, regioselective epoxide cleavage-oxidation, and intramolecular Wadsworth-Emmons cyclization took advantage of highly efficient stereocontrol. However, this flexibility was thwarted when deprotonation of a penultimate intermediate failed to be regioselective in the proper direction.
提出了一种选择性对映体方法,用于构建CP化合物的复杂框架。合成依赖于两个侧链的初步加工。"上部"附属物被不对称地二羟基化,使用两种AD-mix试剂,以赋予方案灵活性,并为发展额外立体中心提供必要的处理手柄。这些片段通过苯甲酸经过桦还原-烷基化和随后的铜化物加成连接。一系列官能团化反应包括溶解金属还原、Claisen重排、碘内酯化、区域选择性环氧开裂-氧化,以及分子内Wadsworth-Emmons环化,利用了高效的立体控制。然而,当一个次末端中间体的去质子化未能在适当方向上具有区域选择性时,这种灵活性被阻碍了。