Your son is a misogynist AND a potential rapist. I don't think you need to do anything for the misogynist part. I think this will change as he knows and discovers how wonderful are women. Which will happen as life goes on. But you absolutely must clarify to him that after "no" he MUST stop. He is free to think low of her, but he must stop.

Read to him what happens to rapists. Check the law. Don't talk to a psychologist, talk to a lawyer.

Suppose you say:

-"...and so you stop".

And he answers:

-"but she is a slut"

Now he is equating "being a slut" with deserving to be raped. This is the problem.

If you now tell him she is not a "slut" he can easily confuse this in thinking you are accepting this connection.

Of course the best would be to convince him that women are not sluts AND that he should not rape all women (regardless of their morality). But while you can easily stop the second, the first takes time. You can hardly convince someone, it must come out of experience.

In our society we do not punish people for their moral behaviour nor for their thoughts. So clarify to him that being a "slut" is not punishable. In the same way you should not punish him for being an "asshole" (sorry). But the law is clear. No rape.

So I would suggest to accept his logic, but clarify the law.

After

-"but she is a slut"

Any answer like:

-"who said no. And. So. You. Stop."

-"even if you think she is a slut, you still need/must stop if she says so"

-"being a slut does not give you permission to rape her"

-"you thinking she is a slut does not give you permission..."

Turn all this around.

Suppose my daughter one time discusses make up a fake rape accusations against a guy because he is an asshole. I would not try to convince her that he is not an asshole. I would clarify to her that she should not punish people for being an asshole, and that she is breaking the law in doing that.

Start with the law. Then you are on stable ground. And then you proceed from there.