3,4-Epoxyprecocenes: thermal and acid promoted dimerisation

Thermal dimerisation of 3,4-epoxyprecocene II ($\text{2b}$) in absence of solvents afforded high yields (65%) of tetrahydrofuran dimer $\text{4}$ and minor amounts of benzopyran-3-one $\text{3}$. On the other hand, two new dimers, γ-hydroxyketone $\text{5}$ and dioxane $\text{7a}$ have also been isolated from treatment of $\text{2b}$ with different acids. Structural elucidations for all these dimers have been carried out by spectroscopic and analytical methods, combined with the use of selected deuteriated precursors in the corresponding dimerisation procedures.