An asymmetric synthesis of the ABCD ring system of daphnilactone B is described. The synthesis features a tandem, double intramolecular, [4+2]/[3+2] cycloaddition of a highly functionalized, enantiomerically enriched nitroalkene to generate a pentacyclic nitroso acetal. The cycloaddition establishes six contiguous stereogenic centers including the critical CD ring junction that bears two quaternary stereogenic centers. Hydrogenolysis of the nitroso acetal followed by amide reduction and cyclization provided the AB rings. The methyl substituent on the A ring was installed in the correct configuration via hydrogenation of an exocyclic olefin in the final step.

中文翻译：

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通过串联、双分子内、[4+2]/[3+2] 循环加载策略不对称合成 DAPHNILACTONE B 的 ABCD 环系统。

描述了 daphnilactone B 的 ABCD 环系统的不对称合成。该合成具有高度官能化的、富含对映体的硝基烯烃的串联、双分子内 [4+2]/[3+2] 环加成反应，以生成五环亚硝基缩醛。环加成建立了六个连续的立体中心，包括带有两个四元立体中心的临界 CD 环连接点。亚硝基缩醛的氢解随后酰胺还原和环化提供了 AB 环。A环上的甲基取代基通过最后一步中环外烯烃的氢化以正确的构型安装。