Syntheses of two naturally occurring monoterpenes with the santolinyl skeleton

Abstract

Artemiseole, an ether isolated from Artemisia tridentata, has been proved to be 1,4,4-trimethyl-6-vinyl-3-oxabicyclo[3.1.0]hexane by an unambiguous synthesis in six steps from 1-chloro-2-methylpropene, and is thus an irregular monoterpene of the santolinyl class. The availability of 3,6,6-trimethyl-5,6-dihydro-2H-pyran as an unexpected minor product of one of the steps allowed an efficient eight-step synthesis from the chloro-compound of (Z)-5-ethylidene-5,6-dihydro-3,6,6-trimethylpyran-2-one to be carried out: this is an irregular monoterpene lactone from Chrysanthemum flosculosum that had previously been prepared only by a fifteen-stage process.