Cyclopropane cleavage of chrysanthemic acid relatives to santolinyl, artemisyl, and lavandulyl structures: acid-catalysed and biosynthetic experiments

Abstract

3-Isobutyl-2,2-dimethylcyclopropylmethanol (dihydrochrysanthemyl alcohol) and related compounds undergo acid-catalysed 1,2-cyclopropane (santolinyl) scission; on the other hand, 2,2-dimethyl-3-(2-methylpropenyl)-cyclopropylmethanol (chrysanthemyl alcohol) and various similar compounds undergo 1,3-(artemisyl) cleavage. Introduction of functional groups into the methylpropenyl side-chain in chrysanthemic-type structures allows acid-catalysed cleavage by a 2,3-(lavandulyl) pathway. Certain of the reactions are potentially useful for alkylation with irregular acyclic terpene units, and for specific-atom isolation in biosynthetic work. Feeding experiments, of Santolina chamaecyparissus with ¹⁴C-labelled sodium 2,2-dimethyl-3-(2-methylpropenyl)cyclopropanecarboxylate (chrysanthemate) and chrysanthemyl phosphates, have been carried out, but no significant incorporation into 3,3,6-trimethylhepta-1,5-dien-4-one (artemisia ketone) has been found. In comparison with incorporations into other monoterpenoids, mevalonic acid is a poor precursor of artemesia ketone.