Which movies should my bf definitely see before Infinity war?

So my bf and me are working through a "top 250 movies" list atm, and infinity war and endgame are on this list. Today our random pick is infinity war.

The thing is, my bf says he isn't really interested in superheroe movies and the mcu movie trailers didn't really look appealing to him so far.

So he is willing to see infinity war without knowing any kind of backstory. He has only seen Spiderman with Toby Maguire.

Do you think there are any mcu movies that are an absolute must-see before infinity war for people who are generally not really interested in superheroes and stuff? I thought maybe Guardians or the galaxy vol.1? Since it's at least about infinity stones (as far as I remember)