Melt the butter over medium high heat in the iron skillet. Remove from the heat and sprinkle the brown sugar evenly to cover the butter. Next, arrange pineapple rings around the bottom of the pan, one layer deep. Place a maraschino cherry into the center of each pineapple ring. Prepare the cake mix as directed by the manufacturer, substitute some of the pineapple juice for some of the liquid in the directions. Pour the batter over the pineapple layer.