I agree with every post @TwinsAndTrifle has made.
I have two children, both of whom are at secondary school, and have asd. The eldest has had issues with bullying and frenemies in primary, but transitioned/settled well at secondary, and has good friends that get her, and accept and like who/how she is.
My youngest has (and has had) huge issues socially, he struggled all through primary, and he would be that little boy walking around the outside of the playground by himself, because no-one wanted to play/chat with him. Not all the time, sometimes he was part of groups, and played etc, but he's extremely intense, and intransigent, and he can be very hard work; tbh a lot of the time most other kids have no idea of what he's monologuing on about. It has taken us years of working on his social skills, us and school, to get him to where he is now- at secondary, able to interact for a decent part of the social time, beginning to make a few genuine friends. We still have to regularly remind him of how to speak to people cordially, and that others need to be allowed to participate in conversations too, but he is improving.
I do not think it's a reasonable request that he sit with this group. He isn't part of their social group, why should he be? Other mechanisms exist for him to pass social time- I would be far more concerned about the small inclusion support groups that aren't working, and pushing for that kind of provision than trying to make other children accept him. That isn't inclusion, it's tolerance, and there's a huge difference there. I don't want my son 'tolerated' thanks- I want him to find his own niche and make genuine connections with people. He desperately wants and needs that too.
Please do consider a different approach.