The chrysanthemumcarboxylic acids. II.—‐Esterification of the chrysanthemic acids

Abstract

AbstractEsterification of (±)‐cis‐ and (±)trans‐chrysanthemic acids in methanolic sulphuric acid gives the expected methyl chrysanthemates together with methyl δ‐methoxydihydro‐chrysanthemates. Normal esterification of the carboxyl group is accompanied, in part, by acid‐catalysed addition of methanol to the ethylenic bond of the isobutenyl group. Methyl (±)‐cis‐δ‐methoxydihydrochrysanthemate is also formed on methanolysis of (±)‐cis‐dihydro‐chrysanthemo‐δ‐lactone.Ozonization of the methyl chrysanthemates, followed by hydrogenolysis of the ozonides, gives methyl (±)‐cis‐ and (±)‐trans‐3‐formyl‐2: 2‐dimethylcyclopropane‐I‐carboxylates in low yield. The (±)‐trans‐aldehydo‐ester is also obtained, though also in low yield, by Rosenmund reduction of (±)‐trans‐3‐carbomethoxy‐2: 2‐dimethylcyclopropane‐I‐carbonyl chloride and by Raney‐nickel hydrogenolysis of ethyl (±)‐trans‐3‐carbomethoxy‐2: 2‐dimethylcyclopropane‐I‐carbothiolate, both prepared from (±)trans‐caronic acid.