Reaction mechanism of salicylic aldehyde and diethyl malonate
The reaction of salicylic aldehyde with diethyl malonate is an important reaction in organic synthesis, which contains a unique reaction mechanism.

The role of base
In the initial stage of the reaction, basic substances need to be introduced. The key role of basic reagents is to capture the hydrogen atom on the methylene in diethyl malonate. Since the methylene in diethyl malonate is affected by the electron-withdrawing effect of two carbonyl groups, the hydrogen atom on it has a certain acidity. The combination of base and this hydrogen atom prompts the conversion of diethyl malonate into the corresponding carbon negative ion. As a nucleophilic reagent, this carbon negative ion has extremely active chemical properties.

Nucleophilic Addition Reaction
The carbon anion of diethyl malonate generated by the nucleophilic addition reaction
performs nucleophilic addition to the aldehyde group of salicylate by virtue of its nucleophilicity. The carbon atom in the aldehyde group is partially positive due to its connection with the oxygen atom with greater electronegativity, and is vulnerable to the attack of nucleophilic reagents. The carbon anion attacks the aldehyde group carbon, causing the carbon and oxygen double bond in the aldehyde group to open, and the electron cloud is shifted towards the oxygen atom, forming a negatively charged intermediate.

Intramolecular rearrangement and dehydration
The above intermediates are not stable, and an intramolecular rearrangement process occurs. During this process, the atoms or groups inside the molecule are rearranged through the breaking and formation of chemical bonds, and at the same time accompanied by a dehydration reaction. After this series of changes, a product with a specific structure is finally formed. The product structure not only contains part of the structural fragment of salicylic aldehyde, but also fuses the structural characteristics of diethyl malonate, so as to realize the construction and transformation of organic molecules. The whole reaction mechanism involves key steps such as acid-base interaction, nucleophilic addition, and intramolecular rearrangement and dehydration, which jointly promote the conversion from salicylic aldehyde and diethyl malonate to the target product.