The oxidation of aldehydes and alpha-diketones with peroxy compounds
The Baeyer-Villiger oxidation is conducted under acidic conditions such as an alkyl peroxide in the presence of a mineral acid (e.g.; H2SO4) or a peracid (e.g.; peracetic acid or m-chloroperbenzoic acid). In the reactions described in the diagram, the reactions of aldehyde 1 or &alpha;-diketone 7 are initiated by proton of the carbonyl oxygen followed by addition of peroxide (an alkylperoxide is illustrated). Ultimately, the oxygen of the RO-moiety is protonated and is the effective leaving group (ROH) in the rearrangement. In both sequences, the red route is favored; the blue route disfavored. Cation 3 is a more stable species than cation 5 because of hyperconjugation with the alkyl group or resonance stabilization if R'=aryl. Cation 3 affords a carboxylic acid while cation 4 would lead to formate ester 6.
In the case of peroxyhemiketal 8, acyl migration leads to cation 9 which is more stable than species 11, which has a positive charge adjacent to a carbonyl group, which is destabilizing. Thus, anhydride 10 is formed in preference to &alpha;-ketoester 12.