We report the first enantioselective total synthesis of diterpenoid randainin D, which possesses a hydroazulenone core with a β-substituted butenolide moiety on the cycloheptane ring. The trans-5/7 ring system was formed via a highly challenging ring-closing metathesis delivering the tetrasubstituted cycloheptenone. The butenolide moiety was installed via a novel deoxygenative allylation under Ir-photoredox catalysis, employing methyl oxalate as a red/ox tag. Moreover, the developed allylation was successfully utilized in the 7-step total synthesis of (+)-barekoxide. This study suggests that this deoxygenative allylation method is a promising strategy for the formation of Cq–C(sp³) bonds (Cq = quaternary center) in the context of natural product synthesis.

中文翻译：

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通过光氧化还原催化脱氧烯丙基化全合成二萜 (+)-Randainin D 和 (+)-Barekides

我们报道了二萜 randainin D 的第一个对映选择性全合成，它具有氢薁酮核心，环庚烷环上有 β-取代的丁烯内酯部分。反式-5/7环系统是通过极具挑战性的闭环复分解形成的，从而产生四取代的环庚烯酮。使用草酸甲酯作为 red/ox 标签，在 Ir-光氧化还原催化下通过新型脱氧烯丙基化安装丁烯酸内酯部分。此外，所开发的烯丙基化已成功用于(+)-barek盐的7步全合成。这项研究表明，这种脱氧烯丙基化方法是在天然产物合成中形成 Cq-C(sp ^{3 ) 键（Cq = 四元中心）的一种有前景的策略。}