Preheat oven to 350°F. Grease a 13x9 pan. In large bowl combine first 6 ingredients stir. Using a pastry blender cut in butter until it resembles coarse crumbs. In small bowl combine buttermilk, eggs, and vanilla. Add to flour mixture all at once, stir just until moistened. Fold in mangoes. Spread in pan.
Combine the 1/3 cup sugar and cinnamon. Sprinkle over batter.