[en] Mixtures of α-Santonin and various solvents were irradiated by either high or low pressure mercury lamps. The photochemical reactions afforded lumisantonin (11) (76% in acetonitrile), (3 S,3a S,9βS)-3,6,6-trimethyl-3,3a,4,5-tetrahydronafto[1,2-b]furan-2,7(Η6,9βΗ) dione (12) (100% in acetonitrile), 10α-acetoxy-3-oxo-1,7αHΗ,6,11αaΗ-guaia-4-en-6,12-olide (8) (26% in acetic acid), 10α-hydroxy-3-oxo-1,7αaΗ,6,11αΗ-guaia-4-en-6,12-olide (10) (32%) and (E)-3-((3 S,3a S,7αS)-3-methyl-2-oxo-6-(propan-2-ylidene)hexahydrobenzofuran- 7 - (7αΗ)-ylidene)propanoic acid (9) (44%) (in water/ acetic acid 1:1, v/v). Lactone 12 was also prepared by irradiation of lumisantonin in diethyl ether. Lactones 8 and 10 were converted, respectively, into the 10 α-acetoxy-3α-hydroxy-1,7αH,6,11αH-guaia-4-en-6,12-olide (13) (87%) and 3a,10a-dihydroxy-1,7αH,6,11αH-guaia-4-en-6,12-olide (14) (75%) by sodium borohydride reduction. The effects of the compounds on the development of radicle of Sorghum bicolor and Cucumis sativus were evaluated. (author)