In comparison with other ethers, enol ethers of all kinds are rather unstable. As alkenes they are also more reactive than normal alkenes because of the lone pair of electrons on the oxygen atom. They react with electrophiles like bromine or chlorine on the α carbon atom, behaving like enol derivatives and not like alkenes. Electrophilic attack occurs at the α carbon atom and the halide ion released in this step then attacks the silicon atom to release the product and a molecule of Me₃SiX, which will be hydro lysed during the work-up.

This procedure avoids the difficulties we outlined earlier in the direct halogenation of aldehydes and ketones. It allows the preparation of haloketones on the less substituted side of the carbonyl group, for instance.

A similar method with the good soft electrophile PhSCl allows sulfenylation next to the carbonyl group.

The mechanism is very similar: the electrophilic sulfur atom attacks the α carbon atom of the silyl enol ether, releasing a chloride ion that removes the Me₃Si group from the intermediate.

مواضيع ذات صلة

Nitration of benzene

Benzene and its reactions with electrophiles

enols and phenols

Reactions of enol ethers Hydrolysis of enol ethers

Enol and enolate reactions at oxygen: preparation of enol ethers

Silyl enol ethers

Nitrosation of enols

The Robinson annelation

Intramolecular aldol reactions

How to control aldol reactions of aldehydes

How to control aldol reactions of esters

Specifi c enol equivalents from 1,3-dicarbonyl compounds