The feeding-deterrent activities of thirteen synthetic terpenoid lactones, including isomeric bicyclic gamma-spirolactones with the limonene system and tricyclic gamma-lactones with the pinane system, were determined towards three storage pest insects: the adults of Sitophilus granarius, the adults and larvae of Tribolium confusum and the larvae of Trogoderma granarium. The configuration of chiral centres, as well as the presence of additional functional groups (double bond, iodine and hydroxy group) are important for antifeeding activity.
Starting from (+)- and (-)-perillyl alcohols, via Claisen rearrangement and iodolactonization, four enantiomeric pairs of gamma-lactones were obtained. The structures of compounds were established by both spectroscopic and crystallographic methods. The lactones were tested for antifeeding activity toward grain storage pests-the granary weevil beetle (Sitophilus granarius L.), the khapra beetle (Trogoderma granarium Ev.), and the confused flour beetle (Tribolium confusum Duv.). The results of the tests proved that two compounds, (1R,4R, 6R)-(-)-4-(1-methylethenyl)-9-oxabicyclo[4.3.0]nonan-8-one (8a) and its enantiomer (8b), are very active antifeedants against all of the above tested species. The lactone 8b is also active against the peach-potato aphid (Myzus persicae Sulz.). The activity depends on the absolute configurations of compound chiral centers. Additionally, the lactones 8a and 8b are characterized by interesting fragrances.
Enantioselektive Erzeugung und intermolekulares Abfangen eines Lithiumcarbenoids erfolgt bei der Reaktion von Epoxiden aus 2,5‐Dihydrofuran, 2,5‐Dihydropyrrol sowie Oxa‐ und Aza‐bicyclo[n.2.1]alkenen (n=2, 3) mit Organolithiumverbindungen in Gegenwart externer chiraler Liganden. Diese Methode kann zur Synthese wichtiger ungesättigter Diole und Aminoalkohole verwendet werden (siehe Schema; NBoc=N‐t‐Butoxycarbonyl).
Four enantiomeric pairs of spirolactones were obtained in a four step synthesis from (+) and (−) limonene. The Claisen rearrangement and iodolactonization were the key steps of the syntheses presented. The structures of products were confirmed by X‐ray crystallography of 11, 18b, and 19.
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