Acid‐Mediated Formation of Radicals or Baeyer–Villiger Oxidation from Criegee Adducts. Issue 40 (12th August 2015)

• Record Type: Journal Article
• Authors: Schweitzer‐Chaput, Bertrand; Kurtén, Theo; Klussmann, Martin
• Is Part Of: Angewandte Chemie international edition. Volume 54:Issue 40(2015)
• Page Start: 11848
• Page End: 11851
• Publication Date: 2015-08-12
• Subjects: Baeyer–Villiger oxidation -- Brønsted acid catalysis -- ketones -- peroxides -- radical reactions; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201505648
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: The acid‐mediated reaction of ketones with hydroperoxides 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. Abstract : At the crossroads : Criegee adducts of hydroperoxides and ketones are key intermediates in the Baeyer–Villiger oxidation, but they can also generate radicals via formation of alkenyl peroxides. The fate of the Criegee adduct is determined by the electronic nature of the peroxide: peracids favor rearrangement, alkylhydroperoxides favor radical formation. Hydrogen peroxide is equally suitable for both pathways, explaining its poorer performances in the two reactions.