A General Synthetic Entry to <i>Strychnos</i> Alkaloids of the Curan Type via a Common 3a-(2-Nitrophenyl)hexahydroindol-4-one Intermediate. Total Syntheses of (±)- and (−)-Tubifolidine, (±)-Akuammicine, (±)-19,20-Dihydroakuammicine, (±)-Norfluorocurarine, (±)-Echitamidine, and (±)-20-Epilochneridine<sup>1</sup>
general strategy for the synthesis of pentacyclicStrychnosalkaloids with the curan skeleton has been developed. It utilizes 3a-(2-nitrophenyl)hexahydroindol-4-one (23), which was prepared from 2-allyl-2-(2-nitrophenyl)-1,3-cyclohexanedione (15), as the common, pivotal intermediate. Three different procedures have been employed for the closure of the bridged piperidine D ring from 23: (i) an intramolecular
已开发出合成具有curan 骨架的五环马钱子生物碱的一般策略。它使用由 2-烯丙基-2-(2-硝基苯基)-1,3-环己二酮 (15) 制备的 3a-(2-硝基苯基)六氢吲哚-4-酮 (23) 作为常见的关键中间体。已采用三种不同的程序来闭合来自 23 的桥连哌啶 D 环: (i) 分子内迈克尔型共轭物加成;(ii) Ni(COD)2 促进的双环化,在单个合成步骤中组装 B 和 D 环,以及 (iii) 烯酮-炔丙基硅烷系统的分子内环化。必要时,根据所使用的程序,在 C-16 处引入氧化的单碳取代基,关闭吲哚环,和/或调整 C-20 二碳链的功能构成了标题生物碱合成路线的最后阶段。涉及炔丙基硅烷环化的过程已成功扩展到对映特异性……
Nickel-Catalyzed Intramolecular C−O Bond Formation: Synthesis of Cyclic Enol Ethers
作者:Seo-Jung Han、Ryohei Doi、Brian M. Stoltz
DOI:10.1002/anie.201601991
日期:2016.6.20
efficient and exceptionally mild intramolecular nickel‐catalyzed carbon–oxygen bond‐forming reaction between vinyl halides and primary, secondary, and tertiary alcohols has been achieved. Zinc powder was found to be an essential additive for obtaining high catalyst turnover and yields. This operationally simple method allows direct access to cyclic vinyl ethers in high yields in a single step.
Palladium catalyzed reductive Heck coupling and its application in total synthesis of (−)-17-nor-excelsinidine
作者:Lisi Yuan、Linrong Chen、Xiaoxiao Yan、Kun Gao、Xiaolei Wang
DOI:10.1039/d1ra00015b
日期:——
Monoterpene indole alkaloids, bearing a highly substituted piperidine ring, are a structurally diverse class of bioactive natural products, found in various parts of the world. Herein, we reported the construction of the key piperidine ring via palladium catalyzed reductive Heck coupling with a good syn selective manner, avoiding the usage of stoichiometric, highly toxic, air sensitive and moisture
developed in continuous‐flow mode, which facilitated the rapid construction of a series of diversely functionalized 2,7‐heterocycle‐fused tetrahydrocarbazoles, the ubiquitous core structures embedded in strychnos and akuammiline‐type monoterpene indole alkaloids. The synthetic utility of this novel method has been preliminarily explored by the first total synthesis of (+)‐alsmaphorazine C and formal synthesis
The Double-Bond Configuration of Corynanthean Alkaloids and Its Impact on Monoterpenoid Indole Alkaloid Biosynthesis
作者:Ruben Eckermann、Tanja Gaich
DOI:10.1002/chem.201505068
日期:2016.4.11
incorporate E or Z double bonds located at C19–C20, the alkaloids downstream in the biosynthesis exclusively exhibit the E doublebond. This study shows that secondary cyclizations preferentially occur with the E isomer of geissoschizine or its derivatives. This is attributed to the flexibility of the quinolizidine system of the corynanthean alkaloids, which can adopt a cis or trans conformation. For