Purified mCPBA, a Useful Reagent for the Oxidation of Aldehydes

Purified m CPBA is a useful reagent for the oxidation of several classes of aldehyde. Although linear unbranched aliphatic aldehydes are oxidized to the corresponding carboxylic acids, α‐branched ones undergo Baeyer–Villiger oxidation to formates. α‐Branched α,β‐unsaturated aldehydes provide enolformates and/or epoxides, which can be saponified to α‐hydroxy ketones with shortening of the carbon chain by 1 carbon. Unbranched α,β‐unsaturated aldehydes undergo an interesting Baeyer–Villiger oxidation/epoxidation/formate migration/BV oxidation cascade, which results in formyl‐protected hydrates with an overall loss of two carbon atoms.