Melt butter and brown sugar in heavy skillet. Add salt, cinnamon and pineapple, and mix well.
Cook over medium to medium high heat until pineapple is cooked through and sauce thickens, about 15 minutes.
Remove skillet from stove and add rum. Flame rum by shaking pan (over gas flame) or lighting with long match. Or, let alcohol burn off over medium heat if not flaming.