Enones provide a solution to regioselectivity problems

In general, this effect is sufficient to allow selective kinetic deprotonation of methyl ketones, that is, where the distinction is between Me and alkyl  

The same method works very well for 2-substituted cyclohexanones the less substituted enolate forms. Even with 2-phenylcyclohexanone, which, as you have just seen, has a strong thermodynamic preference for the conjugated enolate, only the less substituted enolate forms. 

2-Methylcyclohexanone can be regioselectively alkylated using LDA and benzyl bromide by 

Dianions aiiow unusuai regioselectivity in alkylations of methyl acetoacetate 

In Chapter 23, we introduced the idea that the last-formed anion in any dianion or trianion is the most reactive. Methyl acetoacetate is usually alkylated on the central carbon atom because that is the site of the most stable enolate. But methyl acetoacetate dianion—formed by removing a second proton from the usual enolate with a very strong base (usually butyl-lithium)—reacts first on the less stable anion the terminal methyl group. Protonation of the more stable enolate then leads to the product. Butyllithium can be used as a base because the anionic enolate intermediate is not electrophilic. 

Dianions allow unusual regioselectivity In alkylations of methyl acetoacetate 

Dissolving metal reduction of enones gives enolates regiospecifically 

or Li in liquid ammonia, for example) to reduce aromatic rings and alkynes. The dissolving metal reduction of enones by lithium metal in liquid ammonia is similar to these reactions—the C=C bond of the enone is reduced, with the C=0 bond remaining untouched. An alcohol is required as a proton source and, in total, two electrons and two protons are added in a stepwise manner giving net addition of a molecule of hydrogen to the double bond. 

The mechanism follows that described on p. 628 transfer of an electron forms a radical anion that is protonated by the alcohol to form a radical. A second electron transfer forms an anion that can] undergo tautomerization to an enolate. 

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