?The oxidation of ketones with peroxy acids is both novel and synthetically useful. An

Chapter 18, Problem 18.56

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The oxidation of ketones with peroxy acids is both novel and synthetically useful. An oxygen from the peroxy acid is inserted between the ketone carbonyl group and one of its attached carbons to give an ester. First described by Adolf von Baeyer and Victor Villiger in 1899, reactions of this type are known as Baeyer–Villiger oxidations.

       The reaction is regioselective; oxygen insertion occurs between the carbonyl carbon and the larger (R) of the two groups attached to it. Methyl ketones ( R = CH3 ) give esters of acetic acid;

      The mechanism of the Baeyer–Villiger reaction begins with nucleophilic addition of the peroxy acid to the carbonyl group.

    After protonation by an acid catalyst (either the peroxy acid or a carboxylic acid), the conjugate acid of the product of the first step rearranges by an alkyl group migration. Normally, it is the larger of the two groups originally bonded to the carbonyl group that migrates.

    The reaction is stereospecific; the alkyl group migrates with retention of configuration, as illustrated for the oxidation of cis-1-acetyl-2-methylcyclopentane; only the cis product is obtained.

When the ketone is cyclic, a cyclic ester, or lactone, is formed. Cyclobutanone is oxidized to a lactone by the Baeyer–Villiger reaction.

A key step in the laboratory synthesis of prostaglandins involves the sequence shown here. What is the identity of compound X?