Syntheses of (±)-grandisol, (±)-canadensolide, and (±)-fomannosin have been investigated by the use of photocycloaddition reactions of α,β-unsaturated lactones with olefins as the key steps. i) (±)-Grandisol has been stereoselectively synthesized from the photoadduct (3) between β-methyl-Δ^<α,β>-δ-lactone (2) and ethylene-(Fig. 1) ii) Bislactone (14), the precursor of (±)-canadensolide has been obtained from the photoadducts of γ-n-butyl-γ-crotonolactone with 1,1-dimethoxy ethylene. However, attempts to introduce exomethylene group have failed. -(Fig. 2) iii) Synthesis of deoxy dihydro fomannosin has been achieved starting from the photoadduct (19) of β-(4,4-dimethyl-2-oxocyclo-pentyl)-Δ^<α,β>-butenolide to ethylene. -(Fig. 3.4.5.)