Facile HD exchange of the bridgehead methyls of bicyclo[2.2.2]octan-2,5-diones. Evidence for a carbon analogue of the acyloin rearrangement

Hexamethyltwistyl-2,5-dione 4 has been synthesized and its H–D exchange studied in t-BuOK/t-BuOD at 125 °C. We find that the bridgehead methyl at C-3 undergoes exchange 7 × 10 5 times faster than the bridgehead methyl of bicyclo[2.2.1]heptan-2-one (fenchone). This result, along with a previous study, establishes the first examples of the carbon analogue of the acyloin rearrangement of alicyclic systems.