Diastereodivergent Access to cis,cis- and cis,trans-Angular Triquinanes: Total Synthesis of (±)-Arnicenone

Herein, we report a diastereodivergent strategy for stereocontrolled access to both <i>cis</i>,<i>trans</i>- and <i>cis</i>,<i>cis</i>-angular triquinanes from common allene precursors. The <i>cis</i>,<i>trans</i>-fused triquinanes were constructed through a Lewis acid-promoted intramolecular [3+2] Danheiser annulation, whereas the complementary <i>cis</i>,<i>cis</i> frameworks were accessed via photochemical [2+2] cycloaddition followed by oxidative ring expansion.

Notably, substitution at the R¹ position of the allene precursor reversed the diastereoselectivity of the [3+2] annulation, providing direct access to a <i>cis</i>,<i>cis</i>-angular triquinane. DFT calculations indicate that the initial spirocyclization governs both the reactivity and stereochemical outcome of the [3+2] pathway, with substrate-dependent steric interactions accounting for the observed diastereodivergence.