Total synthesis of (±)-cameroonan-7α-ol and biomimetic rearrangements to related nopsane sesquiterpenes
Total synthesis of (±)-cameroonan-7α-ol and biomimetic rearrangements to related nopsane sesquiterpenes
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DOI：
10.1021/jo0343580
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发表时间：
2003-09-05
影响因子：
3.6
通讯作者：
Coates, RM
中科院分区：
文献类型：
--
作者：
Davis, CE;Duffy, BC;Coates, RM
以双环烯酮10为原料，通过巴豆基硅烷的共轭加成、光化学溴氢化、分子内烷基化和氢化物还原等反应，合成了一种新型的硅杂环倍半萜醇（+/-）-cameroonanol（6-OH）.从异构体混合物中分离立体异构体cameroanan-7 β-ol（18-OH）和9-epicameroonanol（19和20），并通过类似的方法获得9-去甲基cameroonanol（21-OH和22-OH）。6-OM和18-OM的溶剂分解影响骨架重排为（+/-）-四氢硅喃-6-烯（5）、（+/-）-异戊烯醇（7）和（+/-）-异戊烯醇（8）以及（+/-）-四氢硅喃-7 β-醇（9），与针对这些天然存在的倍半萜提出的生物遗传方案平行。nor类似物21-OM和22-OM经历溶剂分解反应，得到一组类似的nor产物。与7 α差向异构体相比，7 β-甲磺酸酯18-OM和22-OM的溶剂分解速率的增加归因于prenopsyl和norprenopsyl碳阳离子的协同反周平面Wagner-Meerwein重排。进一步分析的动力学数据和比较与结构相关的硅-1 β-基和硅-1 α-基甲磺酸酯（28和29）的溶剂分解速率。观察到的重排提供化学先例的生物遗传途径在文献中，这些硅杂环己烷倍半萜。
A total synthesis of the novel silphinane sesquiterpene alcohol (+/-)-cameroonanol (6-OH) from bicyclic enone 10 was accomplished by conjugate addition of crotylsilane, photochemical hydrobromination, intramolecular alkylation, and hydride reduction. The stereoisomers cameroonan-7beta-ol (18-OH) and 9-epicamerooonanols (19 and 20) were separated from isomer mixtures and the 9-desmethylcameroonanols (21-OH and 22-OH) were obtained by similar means. Solvolysis of 6-OMs and 18-OMs effected skeletal rearrangements to (+/-)-silphiperfol-6-ene (5), (+/-)-prenopsanol (7) and (+/-)-nopsanol (8), and (+/-)-silphiperfolan-7beta-ol (9) in parallel with biogenetic schemes proposed for these naturally occurring sesquiterpenes. The nor analogues 21-OMs and 22-OMs underwent solvolytic rearrangments to a similar set of nor products. The increase in solvolytic rates for the 7beta-mesylates 18-OMs and 22-OMs in comparison to the 7alpha epimers is attributed to concerted antiperiplanar Wagner-Meerwein rearrangements to the prenopsyl and norprenopsyl carbocations. Further analysis of the kinetic data and comparisons with solvolysis rates for the structurally related silphin-1beta-yl and silphin-1alpha-yl mesylates (28 and 29) are presented. The rearrangements observed afford chemical precedent for the biogenetic pathways in the literature for these silphinane sesquiterpenes.