Have you taught him instead.... how to be a 'sibling?'
That "family" is watching out for each other and taking 'care' of each other?
That she is a baby... and cannot do what he does?
She is not a 'toy?'
I have a sibling that was like that. It was so hard, being at the end of the stick like that.
Once she became an adult, after ALL those many years, she told me that she was actually Jealous of me and resented me. So she took things out on me. Meanwhile, it was really miserable being at the end of her meanness. Sure, my parents did what they could to make her learn. But still, she just erroneously thought, that she was de-throned and that I was the 'favorite' even though that was not true.
Have you ever... just talked 'with' your son, about his place in the family, about his place in your heart, about HIM and what is going on? Have you asked him WHY he does all those things?
Currently, reacting to him and punishing him and scolding him... does not work. Maybe because, there are other issues. And that is why he is so mean to his sister.
At this age, they do know right/wrong. Many kids are in school at this age... and they do grasp basic concepts of meanness and that it is not appropriate.
Sometimes also, an 'Eldest' sibling has SO many 'expectations' upon them... and are 'suddenly' expected to act all 'grown-up'... but they are not. So parental expectations upon them and how they really are developmentally... is not congruous. And then Eldest takes things out on the younger sibling. Taking frustrations out, on another.
I assume he is getting lots of attention. But right now it is 'negative' attention. Maybe he just wants attention. Period. Even if it is via scolding.
And, a 2 year old, is not old enough to defend themselves, intellectually or emotionally. So you have to watch out for her too. It sucks... being in that position. I know. That is how one of my siblings, was. To me.
Instead of reacting to him... try appealing to his emotions/sense of security/sense of self and whether he is getting what he needs. As a child of 4 years old. Maybe he needs more attentiveness? More one on one time? More, of something? Try finding what that is.