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. © 1994, Taylor & Francis Group, LLC. All rights reserved.