i know what you are going through cause im going through the same thing with my 10 yr old daughter it seems to be triggered by the word no
the med seem not to working the older she gets
If you read the post from Dr Kennedy on the post he wrote Discipling a child with Bipolar,every word he says there is correct,read it again, keep doing the time outs if he throws a big fit, thats okay,be consistant and make him stay in time out on a chair,do not get into yelling matches it will only reinforce the negative behavior, if he is on Meds ask if they could cause any further behavioral problems such as you are having .Mostly check what triggers his Tantrums then try not to feed into them making it a power struggle.Take a step back and let him yell, he may give up if he doesnt get any reaction from you.