Five boys - that is rough! He just might not click with any of them if there are only five first grade boys. If he isn't already, I would get him into some activities where he is likely to find peers with similar interests, perhaps even close in age.
Boys this young are pretty simple - one day, they are "best friends" with each other, the next day, one of the same boys prefers playing with another boy because this other child has a video game he likes. They argue and then are great friends again soon after. I do not think your DS should consider himself "permanently excluded" from the first grade boys. As hard as it is, I try to help DS just "roll with it." I tell him that things will be better tomorrow - and usually they are!
DS5, in K, is my more sensitive child. If someone so much as looks at him sideways on the bus, he talks about it for 2 days. He wants everyone to like him, he is a follower, and I worry about him trying "too hard" to blend in with his peers. He is the opposite of my DD this way!
I "help" DS a great deal by allowing him to have friends over often. I indulge his interests that help him relate to his friends. He is still the "sensitive" one, and is academically advanced - it is actually pretty funny to see his friends turn to ask him to read something for them! I see problems possibly ahead, but DS also has a larger group of kindergarteners to chose from - you may need to expand your DS's peer group (chess club, science club, Lego Robotics class?).
I know this is tough, though - DS is sensitive, too!
