Vinylogous compounds are conjugated compounds
A vinylogous aldol reactions occurs with vinylogous compounds.
They operate using key deprotonation and protonation, which force resonation of double bonds across the molecule, making for good nucleophilic carbons.
In basic conditions, an aldol alcohol is deprotonated. The oxygen forms an O=C bond.
The double bonds adjacent to the new carbonyl shift over until they can’t move anymore. This structure looks and resonates like an enolate.
At this point, the extra electrons make for a good nucleophile, and add to another carbonyl (with bad leaving groups).
After this, since there are no good leaving groups on the newly added portion, the negatively charged oxygen is protonated, completing the addition. Below is the general form of this type of reaction.
