I agree with the above poster. I also have a son, six year old, who lives to argue with me, I swear! And with all of the same issues you have, with cleaning his room, doing his homework...heck, he even argues with me when he has to wash his hands before dinner or brush his teeth before bed most nights.
What works to stop the argument just as he starts it is to give a warning, and then follow through with it. For example, we tell our son to clean his room and he has until a certain time to get it done. If it's not done, anything left on the floor goes in the trash. He has lost some expensive and favorite toys that way; sometimes it's even hard for us to follow through because we know it was an expensive toy or a meaningful gift or a favorite of his, but in the end...the value of having an obedient child is worth WAY more. Trust me, when your son sees you trash his toys right in front of him and then take the garbage out to the dumpster, it sends a message loud and clear. All we have to do is threaten to throw away toys now, and our son stops the argument immediately and gets the job done. Every time. He still tries to argue when we ask initally, but all it takes is that warning and the arguing stops.
Homework. Set a timer to get X amount of work done (for example, if math homework, he has to do five problems in 10 minutes). Then he can have a two minute break. If he fails to get X amount of work done in X amount of time, then no two minute break AND he loses TV time and/or more priviledges. If homework is not done before dinnertime, he has X amount of time to eat his dinner before it's taken away and he has to go finish his homework. If homework is not done before bedtime, then he will write a note to his teacher and apologize for not completing his homework even though he had plenty of help and time to do it, and he will sign it. That makes him own take responsibilites for his actions.
Harsh? Yes...
But it sets a clear set of boundaries and respect. Give it a week or two and I'll bet you anything that he will no longer try to argue with you beyond the initial objection once you give the warning.
I also agree with the above poster that you cannot let him make his own punishment. If you send him to his room and he can come out on his own whenever he wants just because he will act sweet is not facing any consequences for the previous behavior. Ground him for the behavior along with sending him to his room, so that the punishment isn't over the moment he decides to walk out the door. Take away TV for a day or two, or a week if the behavior was that bad. Take away a favorite toy or computer or video game time for a few days, or take away playtime with friends on the weekends. If he can't behave and act appropriate around other people when he "doesn't get his way," then he doesn't need to be playing with them until he can understand that you don't always get your way, and if you don't, you have to act appropriately.
sounds like the only thing wrong with him is being spoiled my boys r 6 and 7 when it is time to clean their room i give them 1 hour and if its not done all the toys on the floor go in the trash if they can not pick them up they can not have them and when it comes to homework my boys r not alowed to watch tv or play video games till it is done and they have to try befor i will help them as for the making excuses like drink snack ect try giving him a break time befor homework or what ever tell him ok its time to do ....... u have 10 min to go to the bathroom and get a drink then its time to get started also if timeout lasts untill he comes out of his room and acts better then u r leaving his punishment up to him the next time he starts acting like a brat ground him for the rest of the day (at our house that means no tv games bikes or desert) if a day doese not work make it 3 or a week sometimes u need to use tough love he may say ur mean and he may get mad at u but he is 10 what if he acts like this when he gets old enough to drive and get a job??