Cope Rearrangement - Oxy-Cope Rearrangement

In the Oxy-Cope rearrangement a hydroxyl group is added at C3 forming a enal or enone after Keto-enol tautomerism of the intermediate enol :

for instance in this reaction:

In 1975, Evans and Golob showed that deprotonation of oxy-Cope substrates to form the corresponding alkali metal alkoxides resulted in rate accelerations of 1010 to 1017 for the oxy-Cope rearrangement. Typically potassium hydride and 18-crown-6 are employed in order to generate a fully dissociated potassium alkoxide :

It is noteworthy that the anion-accelerated oxy-Cope reaction can proceed with high efficiency even in systems that do not permit good orbital overlap, as seen in this example from Schreiber's synthesis periplanone B :

The authors remark that the corresponding neutral oxy-Cope and siloxy-Cope rearrangements failed, giving only elimination products at 200 °C.