Tunable Reaction Mode of Bifunctional Peroxides with Ketones to Access α-Oxacyclic Ketones and Enals

A new annulation reaction between allylic/benzylic peroxides and ketones has been developed to provide the α-oxacyclic ketones in moderate yields under the KO^tBu basic conditions. Mechanistic studies reveal that these peroxides undergo the Kornblum-DeLaMare rearrangement to release the aldehyde intermediates and subsequently initiate the aldol/etherification tandem process to deliver the final products. Accordingly, these peroxides serving as "masked" enals have also been utilized to prepare the previously hard-to-achieve α-enal-tethered ketones in one step.