Synthesis of Stereoisomers of <i>Artemisia</i> and <i>Chrysanthemum</i> Bis(acetylenic) Enol Ether Spiroacetals

An 11-step synthesis is described of two diastereomeric candidates for a bis­(acetylenic) enol ether spiroacetal isolated from <i>Chrysanthemum boreale</i>. Key steps in the synthetic route include spiroacetal lactone alkylidenation and subseqent modified Cadiot–Chodkiewicz cross-coupling to install the bis­(acetylenic) enol ether functionality. From NMR comparisons, neither of the candidates, whose structures were confirmed by single-crystal X-ray diffraction, correspond to the natural product, and a proposal for the correct structure is put forward