I agree time out and 'naughty' chairs really aren't a good way to go. Remember at 2.5 he is still learning so many things and one of them is emotional control.
Sometimes he's probably just frustrated or overwhelmed (as we can all be) and it shows by him acting out. Try and catch the triggers early on and get him settled and calm before he gets worked up.
Or else ideas such as sitting with you, cuddles or allowing him some time alone (if it seems he needs that- rather than shumming him like time out) can help. Try not to explain what he's doing wrong when he's in a state- just let him calm down first.
Hope it helps!! Sounds like you're doing a wonderful job!