Aldol reaction is one of the important reactions to form carbon-carbon bonds in organic chemistry. It refers to an organic chemical reaction in which aldehydes or ketones with α hydrogen atoms form enol anions under certain conditions, and then react with another carbonyl compound to generate β-hydroxycarbonyl compounds.

The reaction was independently discovered by Charles Adolphe Woods and alexander porphyrievitch borodin in 1872. Two carbonyl compounds (aldehyde was used in the initial reaction) were connected to synthesize a new β -hydroxy ketone compound.

This kind of product is called Aldol, which is taken from the name of hydroxyl group (ol) of alcohol hydroxyl group and aldehyde (ald) of aldehyde compound.

The aldol reaction can be based on two different mechanisms:

Carbonyl compounds such as aldehydes or ketones can be converted into enols or enol ethers. They are nucleophilic on α-carbon atoms and can attack some active protonated carbonyl compounds, such as protonated aldehydes, which is called "enol mechanism".

Carbonyl compounds or organic compounds containing active hydrogen on carbon atoms can deprotonate at α position of carbonyl group to form enol anions, which are more nucleophilic than olefins and enol ethers and can directly attack electrophiles. The common electrophilic reagents are aldehydes, but the activity of ketones is relatively low. This reaction mechanism is called "enol negative ion mechanism".

Refer to the above content: Baidu Encyclopedia-Aldehyde Reaction