The chemical transformations of α-santonin (1), a C-6 lactonized eudesmanolide, into C-8 lactonized eudesmanolides, i.e., yomogin (2) and four diastereoisomers of dihydrograveolide (36-39), are described. Transposition of 6, 13-olide into 8, 13-olide in eudesmanolides was investigated. Allylic oxidation of the trienone (12) with tert-butyl chromate gave 3, 8-dioxotriene (20) and 3, 6-dioxotriene (22). Reductive lactonization of 20 gave 11α- and 11β-methyl cis-lactones (30 and 31). Yomogin (2) was synthesized from the cis-lactones (32 and 33) by phenylselenenylation and deselenoxylation procedures. Catalytic reduction of 30 and 31 gave diastereoisomers of dihydrograveolide (36-39).