How do I help a 3.5 year old boy to listen?

My son is just the sweetest and wonderful, polite boy. He is awesome in so many ways. The problem is he chooses not to listen and it affects how his whole day goes. He goes to preschool and they will report he did wonderful work but he has difficulty sitting and listening during circle time, when lining up, etc. He is TOTALLY capable of sitting and listening, he does it all day long when engaged in playing with his toys etc. He can attend to tasks for LONG periods of time so it isn't that. It is the choices he is making. Many times he is talking and won't even pay attention to what is asked of him. Then other times, when he is with me, I acknowledge he actually heard me and then doesn't follow through Ex: "If you hear the dog barking can you please help me out and let her in?" (He loves to let her in and out.) Then I hear the dog barkng, more, more and it is raining, I wait to see if he will finally follow through and no. Dog is still outside barking. He gets sent to his room to think about why he is got sent there. He can later tell me what went wrong but he still will do it. He isn't learning that when he doesn't listen, he misses out on things etc. He loves to watch movies, I won't allow any movies and TV and explain, that is saved for people who can pay attention to them and listen to what is going on. When he shows me he can listen I will be glad to let him listen to TV. Hmmmm, doesn't work...TV has been off for 4 days now. Happily send him to have some alone to time "Think about what sent him there." Hmmmmm.....still happening. I know he is 3, But I also know what simple things are expected of him and he is definately making these choices to not listen, not follow through etc. i want to help him but feel I am not being affective. Any suggestions?????? Thank you for your help.