Preheat the oven to 350. Grease a 9x13 inch baking dish.
Cut each apple into 8 wedges and set aside. Separate the crescent roll dough into triangles. Roll each apple wedge in crescent roll dough starting at the largest end. Pinch to seal and place in the baking dish.
Melt butter in a small saucepan and stir in the sugar and cinnamon. Pour over the apple dumplings. Pour Mountain Dew over the dumplings.
Bake for 35 to 45 minutes in the preheated oven, or until golden brown.