A Short Access to the Skeleton of Elisabethin A and Formal Syntheses of Elisapterosin B and Colombiasin A

A short stereoselective synthesis of the Elisabethin A skeleton 4 is described, which opens a formal access to the diterpenes Elisapterosin B and Colombiasin A as well. Key reactions were an intermolecular endo-selective Diels–Alder reaction to generate the decalin part of the molecule, a chemo- and diastereoselective allylation of an aldehyde with allylzinc, a palladium ene annulation of the cyclopentane ring, and a novel sulfonium ylide induced fragmentation of a polycyclic ketone. Additional insights have been gained for the crucial epimerization at C-2.本文报道了一种简洁的立体选择性合成方法，用于构建Elisabethin A骨架4，同时也为二萜类化合物Elisapterosin B与Colombiasin A的形式全合成开辟了可行途径。关键反应包括：用于构建分子十氢萘（decalin）结构单元的分子间endo选择性狄尔斯-阿尔德（Diels–Alder）反应、醛与烯丙基锌试剂之间的化学选择性与非对映选择性烯丙基化反应、环戊烷环的钯催化ene环化反应，以及新型锍叶立德诱导的多环酮碎裂反应。此外，针对C-2位的关键差向异构化过程，本研究获得了更多重要的认知。