[ArcHos]

Hello! I can't understand why base (MeO^-) abstracts proton which is away from halogen. I think that hydrogen on the carbon bearing Cl is more acidic because forming anion is stabilized by conjugation with carbonyl group plus inductive effect of chlorine.

[Guitarmaniac86]

I would expect the methoxide to abstract the proton from the carbon with chlorine as well, but that is assuming it is an enolate mechanism and not a pericyclic mechanism.

Read Clayden page 990-991 for the mechanism and also chapter 36 for some more insight.

[spirochete]

The difference in acidity between the protons is not the point, though. You are probably correct that the side with the chlorine is more acidic. But the deprotonation is reversible, regardless of which side it happens on. There needs to be a productive pathway leading to a product after the deprotonation.