Synthetic studies on O-heterocycles via cycloadditions. Part 2. Adducts from styrene oxides

The styrene oxides (14) and (15), bearing electron-withdrawing functions, readily undergo thermal and photochemical (triplet sensitised) dipolar cycloadditions with simple electron-deficient olefins, regioselectively in the case of methyl acrylate. However, cycloadditions with 5-arylbutenolides as dipolarophiles, required for lignan synthesis, could not be effected in significant yield. A new short route to 5-arylbut-2-enolides was devised. The dihydro- and tetrahydro-furan adducts (18d), (19d), and (20d) all fragment in base to the dienol nitrile (25).