Nuclear magnetic resonance studies. XXXII. Rearrangement, isomerization, and deuterium exchange via β-enolization in bicyclooctenones. A 2H nuclear magnetic resonance study

The equilibration of the α,α -diniethyl derivatives of bicyclo[2.2.2]octenone, bicyclo[3.2.1]-oct-2-en-6-one, and its Δ3 isomer has been examined at 155 and 185 °C in tert-BuO−/tert-BuOH. Using 2Hmr spectroscopy the rates and stereoselectivity of hydrogen–deuterium exchange in each of these ketones have been determined for equilibrations with tert-BuOD as solvent. The relative reactivities for exchange at the allylic and vinylic sites compared to the analogous results for the corresponding olefins reveal a significant activating effect of the carbonyl group. Comparison of the data with those for the corresponding saturated ketones shows that the double bond enhances the rate of isomerization appreciably and increases the bias of the equilibrium toward the [3.2.1] skeleton.