Enol ether formation

Acid catalysed


Enol ethers are sometimes called activated alkenes because of the oxygen lone pair conjugated to the double bond. This donates electrons to form a new double bonded resonance structure: an oxonium ion. Because of this special property, enol ethers are useful in many organic reactions.


A usefull route to preparing enol ethers is to convert an aldehyde into an acetal, then to add a catalytic amount of acid and to remove the excess alcohol (EtOH) by distillation. In the animation methyl groups have been used in place of ethyl groups.

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The start of the reaction almost looks like the hydrolysis of an acetal, however, there is no water to continue this process, so a proton is lost instead. In other words there is no suitable nucleophile for SN1 substitution, so E1 elimination takes place to form the enol ether.