Preheat oven 350 degrees. Prepare yellow cake mix according to box directions but instead of water use the saved pineapple juice from can, you can add extra water to juice if needed. Place butter in a 9x13 cake pan and place in oven till melted. Add and stir in brown sugar and a tablespoon of pineapple juice until creamy. Line pineapple slices in bottom of baking pan till bottom of pan is covered. Mix crushed pineapples in cake batter and pour over pineapples slices. Place in oven till cake is done about 30 to 35 minutes. Let set about 2 minutes then turn pan over a foil lined cookie sheet or dish. Let cool and serve. Its not a pretty cake but it is so delicious.