Photochemical Cycloaddition Reactions of α,β-Unsaturated Lactones with Olefins, and Application to Synthesis of Natural Products

The photochemical cycloaddition reactions of five- and six-membered α,β-unsaturated lactone derivatives with unsaturated substrates (ethylene, acetylene, 1,1-dimethoxyethylene etc.) have been studied. The parent α,β-unsaturated lactone (γ-crotonolactone) and the β-,γ-, or δ-alkyl substituted derivatives add to ethylene and acetylene in the acetone solutions and to 1,1-dimethoxyethylene in the benzene solutions in so good yields as to utilize them practically for synthesis. α-Phenyl-γ-crotonolactone and β-phenyl-γ-crotonolactone also add to ethylene and acetylene, whereas, α-methyl, β-hydroxy, and β-methoxy derivatives do not. As the synthetic applications of the reactions, the synthesis of (±)-grandisol has been achieved, and the synthetic approach to (±)-canadensolide has also been described.