Regiospecific, Enantiospecific Total Synthesis of C-19 Methyl Substituted Sarpagine Alkaloids Dihydroperaksine-17-al and Dihydroperaksine

The optically active tetracyclic ketone 8 was converted into the pentacylic core 14 of the C-19 methyl substituted Na-H sarpagine and ajmaline alkaloids via a critical haloboration reaction. The ketone 14 was then employed in the total synthesis of 19(S),20(R)-dihydroperaksine-17-al (1) and 19(S),20(R)-dihydroperaksine (2). The key regioselective hydroboration and controlled oxidation–epimerization sequence developed in this approach should provide a general method to functionalize the C(20)–C(21) double bond in the ajmaline-related indole alkaloids.

将具有光学活性的四环酮8通过关键的硼卤化反应，转化为C-19位甲基取代的Na-H型山槟榔胺（sarpagine）与阿吗灵（ajmaline）类生物碱的五环核心14。随后将该五环核心14用于19(S),20(R)-二氢白刺新碱-17-醛（1）以及19(S),20(R)-二氢白刺新碱（2）的全合成。本研究开发的关键区域选择性硼氢化反应与可控氧化-差向异构化序列，可为阿吗灵类吲哚生物碱中C(20)-C(21)双键的官能团化提供通用方法。