Preheat the oven to 350 degrees F . 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 smallest end. Pinch to seal and place in the baking dish.
Partially melt butter in a small bowl in microwave 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. Watch them to see how much they're browning . Depending on your oven it make take less time or more . If they seem to browning too much but don't look done in the middle , cover with foil.