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Gastrolactone, a component from the larval defensive secretion of the chrysomelid beetle Gastrophysa cyanea, was synthesized in four steps from citral. The key step was an enal-enamine [2+4] cycloaddition. Gastrolactol, the lactol form of plagiodial, was an intermediate in the synthetic sequence.
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Unelius et al. (1994) studied this question.
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