The acid thermal decomposition products of natural chrysanthemumdicarboxylic acid

Abstract

Thermal decomposition of chrysanthemumdicarboxylic acid (1b) produces a mixture of acidic and neutral products and liberates ca. 0·7 mol. equiv. of carbon dioxide. Separation and identification of the methyl esters of the six acidic products has shown that the acids are cis(Z)- and trans(E)-norchrysanthemic acid [(2a) and (9)], trans(E)-2,6-dimethylhepta-4,6-dienoic acid (5), cis(Z)- and trans(E)-2,6-dimethylhepta-3,5-dienoic acid [(6) and (7)], and 2,6-dimethylhept-3-(or 4)-enoic acid (8); the acids (6) and (7) together constitute ca. 65% of the total acidic product. Thermal decarboxylation of the ¹⁴C-side-chain-carboxy-labelled diacid (18) liberates carbon dioxide containing 13% of the initial activity. The mechanism of formation of the ring cleavage products (5) and (6) is discussed, and the bearing these results have on the stereochemistry of biosynthesis of chrysanthemummono- and di-carboxylic acids (1a and b) is considered.