A 1,2-Wittig rearrangement is a categorization of chemical reactions in organic chemistry, and consists of a 1,2-rearrangement of an ether with an alkyllithium compound. The reaction is named for Nobel Prize winning chemist Georg Wittig.
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The intermediate is an alkoxy lithium salt, and the final product an alcohol. When R" is a good leaving group and electron withdrawing group such as a cyanide (CN) group, this group is eliminated and the corresponding ketone is formed.
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Reaction mechanism
The reaction mechanism centers on the formation of a free radical pair with lithium migrating from the carbon atom to the oxygen atom. The R radical then recombines with the ketyl.
500px|center|The 1,2-Wittig rearrangement reaction mechanism
The alkyl group migrates in the order of thermodynamical stability methyl < primary alkyl < secondary alkyl < tertiary alkyl, this is in line with the radical mechanism. The radical-ketyl pair is short lived and due to a solvent cage effect some isomerizations take place with retention of configuration.
With certain allyl aryl ethers a competing reaction takes place.