Acid catalyzed rearrangements in 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.