It will pass. Sad to say you need to pay him more attention. Remember the 'can you help me with this because the baby is too little and you are soooo clever'.
We had to actually schedule in time to make a fuss of DD so we didn't miss it. . We also got her a few toys that were 'just for you, not for the baby' which she could sit at the table and do (arty things are v popular).
It is really hard and it's harder still not to react when they do this stuff. Make a huge fuss of the baby if he does it as well but pay no heed to him.
I completely sympathise My DS1 (who was 2.4 at the time) was very aggressive towards DS2 (biting, poking in the eyes, trying to tip out of moses basket etc) but it was when DS2 was a newborn. It really is the worst thing as you know why the older one is doing it and torn between feeling for them and their feelings which they have no control over and the baby who is so vulnerable
I posted on here quite a bit as I was so upset about it and wondered how we were going to get through and the general advice is that it will pass....and it did. But it is pretty crap whilst in it.
We started a reward system where DS1 started off each day with a 'good' cup with about 5/6 smarties in it and a 'bad' cup with a couple of smarties in it - if he did something naughty (i.e. hurt his brother) a smartie was removed from his 'good' cup and put in the 'bad' cup and vice versa if he did something really nice. At the end of each day, he could eat the smarties in the 'good' cup. It did work as if he looked like he was going to hurt DS2, we would just remind him about the smarties and he would stop.
I found this phase VERY tough. Dd behaved like this to get my attention and it worked in spades as I would insinctively defend the baby. What did help was making sure that when the baby was asleep I made a big deal out of having special "dd and mummy time" when we did some playdoh or whatever. Also if she attacked the baby I'd try and respond calmly and just pick him up and go somewhere else, ignoring dd.
It passed and I'm struggling to remember how long it went on for - funny how something seems such a big deal when it's going on then the behavious stops and you kind of blank it out .
Totally sympathise. DS is 4 yrs old, DD is 8 mths. He is getting worse if anything , and he gets loads of positive 1-2-1 attention from me, his dad and his granny. He is just insanely jealous of his DD and cannot seem to control himself around her. So exhausting and exasperating.