We had a very similar situation in K, so sorry for your DS.
Agree that a lot of things depend on the culture of the school. Our DS (5th grade now) has several girls among his best friends; they share interests, humor, temperament. However, in K (a different school) this would not have been the case- there was quite a gender divide (probably related to the specific kids, but the culture of the school seemed to reinforce it).
I would certainly let the teacher know what is happening. In our case, the teacher was able to subtly find common activities the boys liked to do together after the bus arrived but before school started (the one I remember best was building with blocks and marble runs). DS was a great builder, and the teacher found ways to point this out to the others, giving him some currency with the boys. (Finding the right activity could be tough- academically DS was doing totally different stuff, and he was not as comfortable on the playground as the others, we were lucky the teacher found a good solution).
We also made efforts to invite the boys individually on playdates or outings; often, once they were one-on-one they were able to find things in common and enjoy each other, and this gradually seeped into the classroom environment. This was tough, particularly for me, as it is hard to put those mean comments and actions aside, but in the end they are little boys and I felt it was important to help DS while he was "stuck" with those particular boys. Things did improve, but we were not sad when we changed schools for 1st😊.