Reactions

First, the base removes an hydrogen atom in α-position relative to the ester to form an ester enolate. This enolate acts as a nucleophile and attacks the carbonyl of another ester, leading to the formation of a tetrahedral intermediate. The intermediate then eliminates an alkoxide, generating a β-keto ester. It is important to note that the proton between the two carbonyl groups is more acidic than that of the starting esters, which leads to the formation of the corresponding enolate due to the excess of strong base used during the reaction. An acidic workup at the end of the synthesis enables the recovery of the desired β-keto ester.