Desacetoxymatricarin (IV), a sesquiterpene lactone found in the genus Artemisia and in the form of 8-hydroxy and acetoxy derivatives in the genus Achillea, has been synthesized from α-santonin by a sequence that allows assignment of the full stereochemistry. The stereochemistry of matricarin (V) has also been determined. The unusual stability to dehydration of some of the cyclopentyl-type alcohols, which were intermediates in the synthesis, is discussed.