The chrysanthemumcarboxylic acids. III.—Lactonization of the chrysanthemic acids

Abstract (±)‐cis‐Chrysanthemic acid is readily lactonized in boiling dilute sulphuric acid to the crystalline (±)‐cis‐dihydrochrysanthemo‐δD‐lactone. The lactone ring is opened by alkali hydrolysis and a derivative of the (±)‐cis‐δD‐hydroxydihydrochrysanthemic acid is obtained. With methanolic sulphuric acid the lactone ring is opened to give mainly methyl (±)‐cis‐±‐methoxydihydrochrysanthemate together with methyl (±)‐cis‐chrysanthemate. In contrast, (±)‐trans‐chrysanthemic acid is converted under similar conditions into the crystalline (±)‐trans‐δ‐hydroxydihydrochrysanthemic acid. The mechanisms of these reactions and their bearing on the Seil and the Wilcoxon–Holaday methods of pyrethrum assay are discussed. On heating at 300° C. in sealed tubes (±)‐cis‐and (±)‐trans‐chrysanthemic acids and (±)‐cis‐dihydrochrysanthemo‐δ‐lactone are converted into an isomeric crystalline lactone, (±)‐pyrocin. This is shown by oxidative degradation not to be a dihydrochrysanthemo‐lactone but to be (±)‐β‐isobutenylisohexano‐σ‐lactone. These lactones are substantially non‐toxic to houseflies.