T.A.
This isn't a cure-all but hopefully you have been teaching him to identify different feelings/emotions. If not, there are great children's books that you can sit down and read during a calm, nurturing moment and ask him, "what do you think that person is feeling?", "How would you feel if that happened to you?" etc.
When he is acting up (don't let it get too far), you can start by labelling for him "it looks like you are angry" or "I'm wondering if you are jealous/frustrated/whatever". None of us like to be told what we are feeling. Ask him if you are correct. Tell him he is helping you figure it out.
Then, go on to asking him when he acts up, "what are you feeling?" The next step is, "what do you need?" Using this method, my 3 year old could tell me that she was bored and needed me to stop working on my school work for a while. By just observing the situation, it would look like she went up and hit her brother for which she would have been disciplined for and caused resentment between us. I would gladly put down what I am doing to help her make better choices instead of just always disciplining their bad choices.
I hope this makes sense - let me know if you have questions. Don't underestimate your child's ability to do this. They will still act up but you are arming them with an important life skill - getting their needs met in appropriate ways. There is no quick-fix.