Determination of Relative Frequency of Carbanion Formation at α-Positions of Ketones under Aldol Reaction Catalysis Conditions

To provide insight into aldol reaction catalysis, the relative frequencies of carbanion formation at each α-position of ketones under catalysis by DBU, proline, β-proline, and related catalysts were determined through the deuteration of the ketones in the presence of these catalysts. For selected cases, the deuteration rate was compared with the aldol reaction rate and whether the generated enolate/enamine resulted in return to the ketone or product formation was estimated.