The Wittig Reaction Forms an Alkene

Therefore, the product of the Baeyer-Villiger oxidation of cyclohexyl methyl ketone will be cyclohexyl acetate because a secondary alkyl group (the cyclohexyl group) is more likely to migrate than a methyl group. Aldehydes are always oxidized to carboxylic acids, since H has the greatest tendency to migrate. 

An aldehyde or a ketone reacts with a phosphoniutn ylide ( ILL-id ) to form an alkene. This reaction, called a Wittig reaction, interchanges the double-bonded oxygen of the carbonyl compound with the double-bonded carbon group of the phosphonium ylide. 

An ylide is a compound with opposite charges on adjacent covalently bonded atoms that have complete octets. The ylide can be written in the double-bonded form because phosphorus can have more than eight valence electrons. 

The Wittig reaction is a concerted [2 + 2] cycloaddition reaction. (Cycloaddition reactions were introduced in Section 8.19.) It is called a [2 + 2] cycloaddition reaction because, of the four electrons involved in the cyclic transition state, two come from the carbonyl group and two come from the ylide. 

The nucleophilic carbon of the ylide adds to the carbonyl carbon while the carbonyl oxygen adds to the electrophilic phosphoms. 

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