Your little guy is so normal – lots of wants and almost no impulse control. His head can process the rules, but his little emotions aren't there yet. Not really his fault – he'll be gradually getting more in control of himself over the next 2-3 years. More of the time, anyway.
Meanwhile, you need parenting techniques that work. I know parents who do well with Love and Logic, The Happiest Toddler on the Block, and 1-2-3 Magic.
My personal favorite, that has been wildly effective with my 4.5 grandson, is How to Talk So Kids Will Listen, and Listen So Kids Will Talk. It coaches you along so you can immediately start incorporating the simple and sensible examples into your everyday situations. The authors, Faber and Mazlish, also have a book called Siblings Without Rivalry that is popular with a few young families I know.
Be aware that not all children respond well to punishment, or even time-outs. Some kids only become more frustrated, reactive and willful until you get to the root of their authentic needs. Otherwise, the needs keep growing, and their ability to cope keeps shrinking.
Good luck. I commend your willingness to keep looking for an approach that works for your son. Kids sure do require us to stay on our toes.