Acid-Mediated Formation of Radicals or Baeyer-Villiger Oxidation from Criegee Adducts

The acid-mediated reaction of ketones with generates radicals, a process with reaction conditions similar to those of the Baeyer-Villiger oxidation but with an outcome resembling the formation of hydroxyl radicals via ozonolysis in the atmosphere. The Baeyer-Villiger oxidation forms esters from ketones, with the preferred use of peracids. In contrast, alkyl hydroperoxides and hydrogen peroxide react with ketones by condensation to form alkenyl peroxides, which rapidly undergo homolytic O-O bond cleavage to form radicals. Both reactions are believed to proceed via Criegee adducts, but the electronic nature of the peroxide residue determines the subsequent reaction pathways. DFT calculations and experimental results support the idea that, unlike previously assumed, the Baeyer-Villiger reaction is not intrinsically difficult with alkyl hydroperoxides and hydrogen peroxide but rather that the alternative radical formation is increasingly favored.