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