Acid catalyzed rearrangements in bicyclo[3.3.1]nonanes : 2-Substituted-6-(1,3-dioxolan-2-yl)-cyclooctanones from 1-substituted-2-hydroxy-9,9-(ethylenedioxy)-bicyclo[3.3.1]-nonanes

Treatment of endo-2 or exo-2-hydroxy-1-substituted ketals 1a–d with p-toluensulfonic acid in dry benzene results in a reversible C₉ bridge cleavage and affords equilibrium mixtures where 2-substituted-6-(1,3-dioxolan-2-yl)cyclooctanones 6a–d are present as main products. Yields in 6a–d are present as the steric hindrance of the substituents at C₁ in the substrate increases as well. Deuterium exchange experiments are in favour of an intramolecular 1,3-hydride shift from C₂ to C₉.