I do not think it would be a first round stoppage unless Wilder landed a lucky punch as Dempsey was a astute fighter, however i do believe Wilder connects with Dempsey's mandible at some point and Mr Dempsey inspects the ring canvas closely. Another opportunity for him to use the phrase he said to his wife after losing the world heavyweight title to Gene Tunney: "Honey, I forgot to duck."
Dempsey would pulverize Wilder. First round...Wilder would hit the mat. Second round...cries for his mama. Third round...Wilder goes to sleep.