Is this a younger 4 yo, or an older 4 yo? There are vast differences between those two ages... One is usually barely out of diapers, while the other is going into PreK. This is going to be long, sorry. I hope it helps some.
I have taught both groups, and have had children just like yours in the past... at that age, when they are verbal, they are acting out for attention almost always. It's different when a non-verbal (2yo or the like) is spitting and hitting, they don't know any other way to get across their feelings - and are in an oral stage still. But a 4 yo, esp an older 4 yo, knows that using physical means to communicate is not acceptable, and that they must use their words to express their feelings. I am assuming you believe he is developmentally up to speed, and not delayed in any way...
I, often, dialogued with my 3yo - PreK students about using our WORDS not our HANDS to show others how we are feeling. We often talked about appropriate ways in which to do so. We did this both in group time, but also in one on one interactions. We did not use timeout in our room for the most part, with PreK students, but encouraged the children to work little tiffs out between each other using their WORDS. Of course, we were preparing them for Kindergarten, I would not use that for children not entering into K soon... your 4 yo may not be that old, yet.
He is crying out for attention in some way... and he's not stupid, either. He KNOWS mom and dad don't give a rip about what he does, and he's not getting any guidance from them on this issue. Because of that, your hands are tied ALOT. Without parental support, we're often helpless, and the kids know that. You can't threaten talks with mom, because he doesnt' care... obviously he enjoys time alone, so that doesn't work either. These children often work through these attention issues as they get older because their peers learn that they dont have to be their friend and play with them... you know? When they reach PreK age, friends become very important, and this child will soon find himself isolated because his classmates will no longer want him near them, and these kind of children often figure out their methods for attention aren't working anymore, and change their ways.
When I had a PreK child that did this, I put them in a quiet area in which they had something productive to work on, but protected my other children. It may not have been discipline to him, per say, but it protected my other children, and that is my job. This child, believe it or not, did quickly tire of playing alone when it become a constant thing. Esp when they are able to see the others playing something fun, that they are not allowed to participate in. I worked to not give the child much attention when they were acting out, but just removed them from the situation and left them alone. I told them that they were choosing to play alone now, because they chose to hurt their friends. It's important to emphasis CHOICES. BUT, when I did see the child doing something good, I doted on them over and over again. Right now, he's getting all the attention when he acts out... why should he change? if he stops, more than likely, he'll just blend back into the classroom and have no more attention than anyone else. more than likely, his parents don't give much at home, either.
I think it comes from a combination of just quickly isolating that child, and ignoring him. Let him play alone, and make sure that no one gives him any attention... when he acts up in group time or in group activities, simply excuse him to his quiet area. Remind him again that he's choosing to not be apart of the group. The other children deserve the activities without his interruption. If he gets ignored enough, he will soon realize that his method is no longer working... just be sure to shower him with positive attention whenever it is merited, above and beyond what you normally give to others. As long as you don't isolate the other children from ever getting special treatments, they will more than likely not even notice you're spending more one on one time with this child, because they don't long for it the same way he does... they are content playing in groups. Find what sparks his interest, watch him play. Bring in something just for him to do, maybe a game just for the two of you, or a book you can read together. There is something that he does enjoy, and once you find that, you can concentrate on building that positive excitement until he becomes so spoiled by that positive attention and the rewards that come with it, that the negatives aren't as appealing.
I would not do any public awards for him that you dont do for other children... if you do something with rewards, you either need to make it completely private between you and him, which is going to be hard with that age, or make it a classwide project. Just because the other children are doing what they are supposed to be doing doesn't mean they should be left out of rewards... everyone should be rewarded for positive behavior, if a few are... you know? At this age, it's very important to be fair.
In the end, if it truly is a daily thing and you give it a few weeks and no headway is made, you need to seriously speak with your director about expelling him. No one wants to do that, but it's not fair to other children and to you to deal with something that you're getting no support on.
Continue to check in DAILY with your director, and even keep a notebook on his behavior each day... note things that strike his interest, things that don't work, how he handles certain situations, things that set him off, people he doesn't mesh well with, etc. Date it, and be specific. if it ever comes to a time in which expellsion is necessary, this will be helpful for the director to present to the parents, and for the parents to read. If they ever show any interest in his daily behavior, it is something you can copy each day and place in his cubby as well.
Good luck to you... Gosh, I have been there and it is so hard to deal with day in and day out. Keep us updated!