An Approach to exo-Enol Ether - Cyclic Ketal Structures Found in Marine Cembranoids, Based on Silver-Assisted Cyclisations of Enynone Precursors
作者:Gerald Pattenden、Johan Winne
DOI:10.1055/s-0031-1290363
日期:2012.3
Treatment of a solution of the (E)-enynone 17 in methanol with AgNO3 leads to cyclisation and isolation of the substituted furan 25 in >95% yield, rather than the anticipated exo-enol ether-cyclic ketal structure 24. By contrast, a similar Ag-mediated cyclisation of the related substituted enynone 20 led to the exo-enol ether-cyclic ketal structure 28 (50%) alongside the substituted furan 29 (45%). The outcomes of these silver-assisted enynone cyclisations are compared and contrasted with earlier studies with acid-catalysed reactions of furanoepoxides, for example 7, which also lead to exo-enol ether-cyclic ketals, viz. 1, and to substituted furanmethanol products, that is, 10.
用 AgNO3 处理(E)-烯酮 17 在甲醇中的溶液会导致环化并分离出取代的呋喃 25,收率大于 95%,而不是预期的外烯醇醚环酮结构 24。相比之下,对相关的取代烯酮 20 进行类似的银介导环化反应,可得到外烯醇醚环酮结构 28(50%)和取代呋喃 29(45%)。这些银辅助烯酮环化反应的结果与早先对呋喃环氧化物(例如 7)进行的酸催化反应研究进行了比较和对比,后者也能生成外烯醇醚环酮(即 1)和取代的呋喃甲醇产物(即 10)。