Preheat oven to 350 degrees F. Spray a 9 by 5-inch loaf pan with cooking spray and set aside.
Remove 3 pineapple slices from the can and reserve the juice and set aside. Chop remaining pineapple slices into small pieces and set aside.
In a large bowl combine the cake mix, eggs, and 1 can of pineapple juice. Blend with an electric mixer on low speed for 30 seconds. Scrape down the sides of the bowl and beat for 3 minutes on medium speed. Stir in the chopped pineapple and combine well. Pour into the prepared loaf pan.
Bake in the preheated oven until a toothpick, inserted into the center of the cake, comes out clean, about 45 to 50 minutes. Remove and cool completely.
In a small pot over medium heat combine the reserved pineapple juice and 1/4 cup of water. Add the brown sugar and butter and bring to a simmer. Add the remaining 3 pineapple rings and saute for 4 minutes or until the sauce thickens slightly. Remove from the heat. Reserve.
To serve, remove the pound cake from the pan and transfer it to a serving plate. Arrange pineapple rings on top and secure with toothpicks, if necessary. Pour the sauce over the cake and serve.