One-Step Stereospecific Strategy for the Construction of the Core Structure of the 5,11-Methanomorphanthridine Alkaloids in Racemic as well as in Optically Pure Form: Synthesis of (±)-Pancracine and (±)-Brunsvigine
作者:Ganesh Pandey、Ravindra Kumar、Prabal Banerjee、Vedavati G. Puranik
DOI:10.1002/ejoc.201100601
日期:2011.8
asymmetric version of the cycloaddition using a chiral dipolarophile was applied to construct the core structure 68 with 63% ee. This strategy was successfully applied to the formal synthesis of (±)-pancracine and the total synthesis of (±)-brunsvigine. An unprecedented and interesting skeletal rearrangement product 49 was observed during the attempted assembly of the E ring from 46 through Horner-Wadsworth-Emmons
复杂的五环 5,11-甲基吗啉嘧啶的独特核心结构通过非稳定偶氮甲碱叶立德 (AMY) 的分子内 [3+2] 环加成一步立体定向构建,AMY 是通过使用 Ag 对 14 进行连续双脱甲硅烷基化生成的IF 作为单电子氧化剂。在关键步骤中单一非对映异构体的形成可以通过 AMY 对偶极体的“Re”面的内切攻击产生的首选过渡态来解释。应用使用手性亲偶极体的不对称环加成形式来构建具有 63% ee 的核心结构 68。该策略成功应用于(±)-pancracine的正式合成和(±)-brunsvigine的全合成。在从 46 到 Horner-Wadsworth-Emmons 反应组装 E 环的过程中,观察到了前所未有的有趣的骨架重排产物 49。涉及氮杂环丁烷盐形成或 Grob 型碎裂的机制被提出来解释观察到的重排。