Sensitized photooxygenation of β-methoxystyrene and 1-(β-methoxyvinyl)naphthalene

Single oxygen can easily add to 1-(β-methoxyvinyl) naphthalene ($\text{1}$) with retention of sterochemistry to afford a stable 1,4-endoperoxide $\text{3}$. Sensitized photooxygenation of β-methoxystyrene ($\text{2}$) gives mainly Diels-Alder adducts of $\text{o}$-formylmethide quinone ($\text{12}$) which might be derived from initially formed 1,4-endoperoxide $\text{10}$.