In the first step, the enolate of an aldehyde, ketone or dicarbonyl compound attacks in a conjugated manner to an alpha,beta-unsaturated ketone.
In a second step the enolate, formed in the conjugated addition, intramolecularly attacks the carbonyl that started the reaction. A very stable six-membered ring is hence produced leading to a cyclohexenone after the usual dehydration that takes place in aldol condensations.
