13C magnetic resonance studies. 144. An examination of β-enolization in the bicyclo[3.3.1]- and [3.2.2]nonan-2-one system

While 3,3-dimethylbicyclo[3.3.1]nonan-2-one (5) is stable under strongly basic conditions (t-BuO−/t-BuOH/185 °C), its isomer, 3,3-dimethylbicyclo[3.2.2]nonan-2-one (6), is slowly transformed to 5. Similarly, 3,3-dimethylbicyclo-[3.2.2]non-6-en-2-one (8b) rearranges to a [3.3.1] isomer but the latter is not stable. Experiments with 3,3-dimethylbicyclo[3.3.1]non-6-en-2-one (7) revealed that it is converted to five compounds, none of which is 8b. The major product, 8,8-dimethylbicyclo[4.3.0]non-1(6),-en-7-one (11) arises from β-enolate rearrangement. Enone 11 undergoes slow reduction to cis- and trans-8,8-dimethylbicyclo[4.3.0]nonan-7-one, presumably by single electron transfer. Experiments with 11 alone showed that β-enolate rearrangement of 7 → 11 is unidirectional. Haller–Bauer cleavage to acidic products occurs as a minor process in the reactions of the unsaturated ketones. The structures of the products were established primarily from their 1H and 13C magnetic resonance spectra.