Rearrangements of pinane derivatives. Part 9. 8,8-Dimethyltricyclo[5.1.1.02,5]nonan-2β-ol, a tricyclic pinane derivative

Abstract

Acetolysis of the toluene-p-sulphonate ester of 2-(2-hydroxyethyl)-6,6-dimethylbicyclo[3.1.1]hept-2-ene (nopol)(1; R = OH) gave a good yield of the acetate of the previously unknown tricyclic pinane derivative 8,8-Dimethyltricyclo[5.1.1.0^2,5]nonan-2β-ol (4a). This molecule has a bridgehead hydroxy group, and so is remarkably stable to acids, despite being highly strained from having two cyclobutane rings. However, the hydroxy group is adjacent to the new cyclobutane ring, so that (4a) is readily oxidised to the acetate of the hydroxytetrahydrofuran, 2β-hydroxy-8,8-Dimethyl-10-oxatricyclo[5.1.1.1^2,5]decane (5; R = OAc). Hydrolysis of the acetate group, followed by oxidation of the alcohol (5; R = OH), yields 8,8-Dimethylbicyclo[5.1.1]nonane-2,5-dione (6).