Total Synthesis and Repudiation of the Helianane Family

Abstract

Total syntheses of two structures purported as (+)-heliananes were completed in six pots. Spectral comparisons, between the synthetic and natural compounds, revealed a misassignment of the eight-membered ring in the heliananes. The key step in the syntheses of the proposed structures and the confirmation of their actual structures was a diastereoselective inverse-demand Diels-Alder reaction between an optically active enol ether and an ortho-quinone methide species, which was generated in situ at low temperature by the sequential addition of methylmagnesium bromide and di-tert-butyl dicarbonate to a salicylaldehyde.

Natural sesquiterpenoids

“…94 The biotransformation of (+)-(S)-ar-turmerone and (+)-(S)-dihydro-ar-turmerone by Aspergillus niger has been studied. 112 In this work, the structures of two compounds 131 and 132, previously isolated as a mixture from Argentinean Baccharis species, have been confirmed. 97 Enantioselective syntheses have permitted the revision of the structures of helibisabonol A and helibisabonol B as the 7R,10R derivatives 123 and 124, respectively.…”

New strategies for natural products containing chroman spiroketals

“…The latter furnished oxazine 27 . Next, we provided the first example of an asymmetric cycloaddition of an o -QM intermediate [9]. Addition of PhMgBr to aldehyde 28 in the presence of enol ether 29 afforded the cycloadduct, 30 .…”

Applications ofortho-Quinone Methides in the Synthesis of Natural Products

“…于是 Trauner 及其同事们提出可以 利用 Hydroxyviocristin (53)原位生成 o-QM 中间体和 Isoechinulins 55a, 55b 经过串联仿生 Hetero-Diels-Alder reaction 和氧化反应构建目标天然产物的分子骨架螺环 N,O-缩醛结构 [35] . 2.8 o-QMs 在 Heliananes 家族天然产物合成工作中的 应用 2011 年 Pettus 课题组 [39] 报道了天然产物 Heliananes 家族的合成工作, Crews 等 [40] 在众多来自自然界的天然产物中, 含有四氢苯并吡 喃多环母核结构的很多天然产物都具有很好的生物活 性, 有些被用于降血压药, 还有些因其具有良好的细胞 毒性而具有被开发为抗癌药的潜力 [41] . 因此如何对这 类天然产物进行全合成也成为了众多化学家关注的热 点.…”