"Reductions of α,β-unsaturated ketones with solutions of Li, Na, or K in liquid NH3 are chemoselective, resulting in the exclusive reduction of the carbon-carbon double bonds. … The regiospecific generation of enolate ions from α,β-unsaturated ketones is an important tool in carbon-carbon- bond-forming reactions. Catalytic hydrogenation of an enone would not be chemoselective if an isolated double bond were also present in the molecule. However, isolated double bonds are inert to dissolving metal reduction. On the other hand, a variety of functional groups are reduced with alkali metals in liquid ammonia. These include alkynes, conjugated dienes, allylic, or benzylic halides and ethers. Nonconjugated ketones can be reduced in the dissolving metal medium to the corresponding saturated alcohol in the presence of excess alcohol prior to workup."
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Hydrogenation
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