Reaction of enols with electrophiles
The functional group in question is a vinyl alcohol, and it is a mistake to consider these groups as isolated. The oxygen is in conjugation with the vinyl group, meaning that resonance favors the entire system attacking. There is no way to leverage conjugation as an energetic driving force if the oxygen attacks by itself.

This is almost the same as your other question: 

Hydrolysis of 3,4-dihydropyran