Investigation of the aerial parts of Artemisia umbelliformis afforded the new eudesmanolides 5-desoxy-5 hydroperoxytelekin and 5-desoxy-5-hydroperoxy-5-epitelekin. A conformational study of the latter and some transformation products showed that these cis-decalin-type eudesmanolides exist in solution at room temperature as single preferred rotamers whose conformation depends on the substituent at C-5.