Pour 1 tablespoon melted margarine in the bottom of a 9-inch springform pan. Combine brown sugar and cranberries; arrange in a single layer over margarine.
Cream 1/4 cup margarine and 1 cup sugar, beating at medium speed of a mixer until well-blended. Add eggs, one at time, beating well after each addition; add vanilla. Combine flour, baking powder, and cinnamon; stir well. Add dry ingredients to creamed mixture alternately with buttermilk, beginning and ending with dry ingredients.
Spoon batter evenly over cranberries. Bake at 350° for 45 minutes or until a wooden pick inserted in center comes out clean. Invert cake onto a serving platter.