Enamine alkylation offers an advantage over direct alkylation of carbonyl compounds primarily due to increased selectivity and reduced polyalkylation:
Carbonyl compounds can be prone to overreaction during direct alkylation, resulting in multiple alkyl groups attaching to the same carbon, complicating the purification process and reducing the yield of the desired monosubstituted product.
Enamines, which are formed by condensation of secondary amines with carbonyl compounds, are less reactive than enolates and thus reduce the risk of such overreaction. In addition, enamines are more easily deprotonated than carbonyls, allowing for more controlled reactions with alkyl halides, ultimately resulting in higher selectivity for single alkylation products.